(More politically: A "liberal" society composed of overlapping subcultures with different norms, in a context of individual rights and social support, seems to be almost certain to meet more people's needs than a "totalizing" society with a single set of norms.)

This works best if none of the "subcultures with different norms" creates huge negative externatilies for the rest of the society. Otherwise, some people get angry. -- And then we need to go meta and create some global rules that either prevent the former from creating the externalities, or the latter from expressing their anger.

I guess in case of BDSM subculture this works without problems. And I guess the test of the polyamorous community will be how well they will treat their children (hopefully better than polygamous mormons treat their sons), or perhaps how will they handle the poly- equivalents of divorce, especially the economical aspects of it (if there is a significant shared property).