1. Marriage is not an "artificial construct." That is, it is not an ersatz substitution for something that is "real." Marriage of some kind is found in just about every culture, primitive or advanced, on earth. Indeed, it is a cultural construct that exists for several important reasons.
2. Marriage protects the rights of children. It defines their responsible guardians, their inheritance rights, their relationships to extended family, etc.
3. Marriage provides a legal framework for property rights between spouses, their children, and extended family.
4. Marriage provides a legal framework for how people behave with each other and for their mutual responsibilities to each other.
5. Marriage provides social context. It is a relationship between two people that defines not only their mutual relationship, but how they relate to society in general. It is also an economic unit within the greater social environment.
Has marriage historically embodied gender inequality? Yes, but things have changed and continue to change. Can you be a legal guardian without being married? Yes. Can you designate heirs without being married? Yes. So what? There's diversity and flexibility in modern society, as there should be.
We have a friend who lived with a woman for 26 years without being married. She died in a car accident. Her children inherited the house and he was evicted, left with nothing from his lover. This is reality, folks. Then again, nobody is forcing you to get married.
I've been married to my INFJ wife for 33 years. We love each other now as much, or more, than ever. We've weathered terrible stresses together, ranging from my wife's medical residency (before they limited on-call hours), to the risks I took starting three businesses, to years-long contract (business) law suits (we prevailed). We've raised two sons who are happy and successful. We've regularly put ourselves in situations that were beyond our comfort zones and at odds with our personalities because one must do so to get anywhere in life. Life is full of stress, but having a life-long, loving, intimate relationship is one of the great comforts and supports in life. In general, married people are healthier, happier, and economically better off than unmarried people.
Many people disparage and deprecate marriage. I think some have had bad experiences from which they unfairly and unreasonably generalize. Others are afraid of marriage and the commitments it entails. Some people have the totally unrealistic expectation that one's partner must fulfill all their expectations and accommodate all their needs (if this were the case, who would need friends?). There are many ways to criticize the institution of marriage, yet it persists. If marriage were unimportant and of no use, it would die. But, people keep trying.
Marriage is not for the self-centered or the immature. To be happily married, it helps to listen, to share values, to pick your battles carefully, to be kind, and to take joy in your spouse's success. Finally, it helps to be lucky.
ed: One last bit. It's better to get divorced before marriage.