I don't think there's any harm in going out of your way to fit in with others. As humans, we are naturally social creatures who seek to form bonds with others. As such, yes sometimes I'll say or do things I don't really feel in order to go along with the group. But if I REALLY disagree with what's being said, I'll make my point (politely and calmly) and stick to it, and if I REALLY don't want to do something, I'll make my excuses and leave quietly rather than make a scene.
BTW, it is possible to be true to yourself and others without upsetting people. Too many people use the cloak of "being myself" or "speaking my mind" as an excuse to be rude or offensive (Alansugaritis, I think it's called). With a little bit of thought, it's not that difficult to find a way to get across the message of what you really think without making people feel stupid or looked down upon.