Assuming 100% isolation it would be indistinguishable from living in a universe where the Many Worlds Interpretation is true, but it still seems wrong. The FAI could consider avoiding groups whose even theoretical existence could cause offence, but I don't see any good way to assign weight to this optimization pressure.

Even so, I think splitting humanity into multiple groups is likely to be a better outcome than a single group. I don't consider the "failed utopia" described in http://lesswrong.com/lw/xu/failed_utopia_42/ to be particularly bad.