You are correct about the in group-out group thing. It seems like the negative energy that is the flipside of positive attachment has to go somewhere. I wonder though if there is a way to just keep expanding the ingroup until it encompasses everyone.
I don't agree with ditching content in favour of harmony/community whether it is a religious organization, an association or a forum. On the other hand I realize that people can get lazy and generalize much too broadly or can become obsessed with focussing on differences. It seems to me though that there has to be an alternative solution rather than just saying it doesn't matter at all.