The reality is that if words have no meaning other than whatever you decide is a good idea at the time then its impossible to communicate.
Words have meaning, you may not like that, you may think it ought to change but you can not in good sense and all honesty suggest that they have no meaning. Surely if you think the word's meaning should change you can make an argument and support it.
If you dont believe words have any meaning and that those meanings are not, at least relatively, fixed then what about words such as homosexual or heterosexual?
I'll be honest and I encounter this sort of sloppy thinking when people are being guided by hopes, best intentions etc. and engaging in lots of emoting. I would not argue with the end of hoping to support and promote love etc. etc. etc. etc. etc. Who could? Its kind of hard to argue with the end of "lets make things better, good for this or that underdog, correct this or that legacy of historical oppression", although I really dont believe simply because the end is defensible that there has to be uncritical acceptance of anything and everything which is suggested as a means to reach that end.
When so called gay rights are in question I think the end is vague to a fault to begin with, however I also think the means which I have heard debated, redefining the meaning of marriage, denying it has any meaning to begin with or denying it has any meaning other than what the popular kids say (which is the sort of high school logic I think is in play here), are ill considered in extremis.
Its all making it increasingly difficult to be critical about attacks on heteronormativity without being labelled a bigot or having it some other way conflated with hatred, its not a good thing, not least because the majority of people are heteronormative by nature and always will be. Think about the amount of neuroticism created by repression of sexuality or the repression of homosexuality and multiple that by about the power of 100,000.
Words have no inherent meaning in the sense that their connection between their sounds or written symbols and their meanings is completely arbitrary. A word has a meaning that is defined only by the consensus of a group of users of the language, not because it has a soul or some other essential, fundamentally unchangeable element. The meanings of words change historically: a particular word might mean something completely different now than what it meant 300 years ago, as we can see when we find an "archaic" meaning in a dictionary — this meaning no longer has currency, it is no longer recognised as having validity in usage by the community of language speakers, it can't be used. In the broad scheme of history, that is a very rapid change rate. The meanings of other words may be even be completely lost; in some very old documents, before dictionaries ever existed, we can discover a word that has been preserved in that document but can be found nowhere in any other printed source in a language, and we have no real way of determining its meaning apart from guesswork, because that unbroken sequence of letters no longer has any meaning in its disembodiment from its cultural historical context — there is no meaning inherent to that letter string, which was once a word. Dictionaries are never "finished" or "complete" compilations, they are only a series of editions of a carefully approximated reference guide that is always necessarily in a process of compilation, because the meanings of words are constantly changing. Definitions of words are always slightly different from one dictionary to another, so that one person using a word may have obtained their definition of the word from one dictionary, while another user of the word may have obtained their definition from another dictionary, and so they have slightly different definitions of the word, which in the confusion of differently-defined exchanges between them, may even inadvertently cause the creation of other meanings that are taken up by one or the other or both. Sometimes a word is used by a person who did not derive their understanding of the word from a dictionary, but from usage contexts, and so they might have a very informally defined and conceptualised understanding of the word, with perhaps highly irrational connotations, which might nevertheless spread through communication with other language users, and to even more users, until it is widely understood in usage in a way that people actively use it to refer to those irrational appendages to it. If these other meanings spread widely in usage and gain enough currency, people compiling dictionaries will need to add those new meanings to the definitions in their dictionaries — but their dictionaries are always following behind the usage in time, documenting the facets of usage after they have happened. It is in usage that word meanings are first formulated, and dictionaries follow after, while meaning constantly continues to change in usage - there is never at any time a state in which the connection between a word and its meaning is "pure". Compilers of dictionaries might employ different research methods in determining usage of words, such as different data analysis programs that sift through language represented on the internet for example — but language is not always documented on the internet (or elsewhere), it is also spoken. And these different methods of collecting data on definitions as expressed in usage may gain access to only particular parts of written and spoken language usage communities but not to other parts, not only so that definitions between dictionaries may be even more various, but so that definitions of words may not actually reflect their meanings that are being formulated through the way that people use them. And then, additionally, dictionaries only have words with which to define other words, and all of their definitions of other words (defined yet again by more other words!) being slightly different, means that language is a very messy system for communicating meaning.
Does this mean that communication in language is impossible? No — for practical purposes of communication it means that communication in language is problematic, and that even when people demand constant clarification of communications, misunderstandings and miscommunications of intended meanings proliferate wildly. For philosophical purposes, and in response to previously stated arguments, what it means is that the notion of inherent stability of language is an illusion, and this means that language is not a stable foundation for insisting on continuation of meanings on the basis that they are not subject to change; they change all the time. It is not enough to say "this word must continue to be defined in such a sense because that is how it is defined", because the only sense that it means what it currently means is the sense in which it has previously been used to refer to particular meanings historically, and in which it is used to refer to those meanings in current language. Saying "marriage is defined as being between a man and a woman because that is the way it is defined", means nothing as an argument as to why it should be continued to be defined that way, because there is no inherent stability in word definitions. There is no fixed or permanent connection between a string of sounds or letters and the meanings that become attached to them through the usage consensus of a community of language speakers. Words mean only what they mean in current usage, their meanings have no inherent immortality, so it is worthless to insist that they continue to be defined in certain ways on the basis of supposedly immortal definitions.
The more pertinent problem with the word "marriage" of course is not just that it has a meaning in more informal registers of usage, but that it has a meaning that is formally legally enshrined in the institutions of our societies. This means that "marriage", as it is legally defined, represents a separate and distinct set of legal characteristics from "civil union". If they are equal, then why is it necessary to have two separate sets of laws for people who are heterosexual, and people who are not? People who are not recognisably heterosexual contribute to their societies through work and taxes just as much as heterosexual people do, and observe the other contracts of their societies such as refraining from wantonly killing other members of society, just as much as heterosexual people do. They are just as able to form consent for the purposes of entering into a legal contract, as they demonstrate by signing countless legal contracts throughout their lives, such as employment agreements, property purchases, credit card swipes, or whatever. So why are people who do not identify themselves as heterosexual being excluded from that legally enshrined institution that heterosexual-identifying people are permitted to have access to?
It seems that the only thing that is consistently recognisably different between the relationships of people who are heterosexual and those who are not is the genitalia of the participants in the relationship. If marriage is defined by the genitalia of its participants, what is the value of preserving it as an institution of society? What is so important about preserving an institution that is defined by the touching together of male and female genitalia? How does that validate the value of loving relationships to society? Because if it's so important, then any heterosexual one nighter might as well be celebrated with marriage. If it is especially for the purposes of producing children that have been formed by the interaction of male and female genitalia, then why do we allow and even expect or encourage longterm heterosexual couples to marry who may have no absolutely intention whatsoever of producing children? Why do we not only permit people to marry who have proved that their union is reproductive?
If it is not on the basis of genitalia and related biological functions that we determine eligibility for marriage, then is it on the basis of some higher emotion - love? And if so, what is it about the love between a man and a woman that is different from the love between a man and another man, or between a woman and another woman, or between an intersex and a man, or between an intersex and a woman, or between an intersex and another intersex? What makes that love between a man and a woman more deserving of access to special legal status than those other loves? How do we objectively determine that the love of those non-heterosexual couples lacks some additional element that makes heterosexual love worthy of access to that institution of marriage? Or, alternatively, how do we objectively determine that the love of the non-heterosexual couples contains some additional element that makes their love unworthy of permitting them access to the institution?
If it isn't the differences between their genitalia or their love that provides valid reason for their exclusion from the institution, then what is it? What makes them so different from heterosexual couples that they must be denied access to the institution of marriage?
I have found it extremely difficult to comprehend your final paragraph. Clearly this isn't any fault of my own, as I have been certified in my competence to interpret English textual forms by an internationally respected research university. It is equally clear that it is no fault of yours in forming language, since you yourself have been sufficiently competent in its usage to determine my own incompetence to interpret literary fiction or to engage with English language on the level of a native speaker (which is exactly what I am). Perhaps language as a communication tool is too unstable for us to ever truly understand each other? What I have managed to glean from your final words is that there is some sense in which the requests of gay or lesbian or intersexed people to be included in an institution that is currently the exclusive domain of heterosexual couples constitutes some sort of an attack on heterosexuality or heteronormativity. How does it in any way affect the access of heterosexual people to an institution to which they already have access, to permit these other couples to have access to the institution? Unless it constitutes an attack in a sense that it compromises the absolute dominance of a majority sexuality on societal institutions. If so, why is it important to maintain this institutional dominance of the majority sexuality, and its biological prerequisites? There's always going to be more heterosexuals anyway, and so heteronormativity is always going to be "normal". So why should heterosexuals be threatened by the idea of sharing access to legal and cultural institutions?