By "chameleonism", do you mean the ability to fit into different social situations? I've found I can respond adequately to "small talk" in various situations though I may not really care about either the topic or the person/people doing the talking. Or I can often find excuses to avoid a conversation I don't want to have. Or, I guess I could fake knowing what I'm doing or what I'm talking about in some situations. Are these the kind of things you mean?
Yes, I do feel comfortable enough with some people to share some inner desires unexpressed, but I don't think there is anyone I've ever felt completely comfortable with expressing everything inside. It's just not feasible or appropriate in any situation I can think of. I guess in the past that bothered me, but now I feel no problem holding some things private to myself and not having anyone ever know.
Yes, I have had my efforts to fit in exposed before. I think the most common situation for that is politics. I am friends both IRL and online with those who are either left leaning or right leaning, and usually the two don't mix, but occasionally ways I've acted while in the company of one group were picked up on by members of the other group, who then wonder if I really agree with them or not. I don't personally think I'm being overly mercurial, but I can understand when the two camps are so rabidly against each other that any interaction with the other camp is seen as disloyal or dishonest.
As to why and what purpose, I guess my feeling is to keep peace. I think that can go into the extreme of conflict avoidance, and I've definitely been like that before. But in the best cases it's merely using words to even out the friction that actions can cause. I really think actions "speak" louder than words, and so my actions represent my true feelings on various things. However, whatever my true feelings on something, such as politics, for instance, I do not see any reason to get into an emotional and unyielding debate with others all the time. It's just a waste of time... If you're going to vote one way or the other, and the debate never introduces new information, just rehashes the talking points on both sides with varying degrees of emotional nonsense, then why not just divert the energy that would be spent debating into working together on whatever you do agree with, even if it is just the weather? It's not conflict avoidance if the conflict isn't productive in any way, it's just waste-of-time avoidance.
Like I mentioned above, I think this used to bother me. I worried that if I didn't "stick up" for my beliefs, then what is the good of having them. But over time I decided that the only things that count in standing up for something are actions, words are just air. So now I do not think it morally wrong to share idle chatter with someone whose actions or beliefs are repugnant or stupid. I don't really have a problem talking about the weather with someone who has proven themselves to be a boob in debates before. I'm OK with paying lip-service to someone's irrational anger or fear or utter ignorance. When it comes to taking action, I act with my heart.