"Belief", and by this I am assuming you mean religious or spiritual belief, is not nearly the only divider. Political views, cultural differences, distribution of wealth, arbitrary distribution of genetic traits that are perceived beneficial, birth into areas of greater or fewer resources, gender/sex, social aptitude, and physiological fitness (to name a few of the more obvious ones) are all used as dividers by human beings. Religion just happens to be the most unnecessary, or least intrinsic... i.e. the most useless, of the dividing criteria we impose.
Nothing is ever going to satisfy everyone, because everyone is too busy being white/black/Asian/etc. or Italian/French/American/Korean/etc. or fit/fat/average/etc. or pretty/ugly/mediocre/etc. or rich/poor/middle-class/etc.
We're all too "self" (whatever that may encompass) to realistically entertain ideas of universal acceptance. And I include myself in this... I don't pretend to be "above it all." There have been too many times I have had the thought cross my mind: "Yeah, we could all get along, if everyone would just accept 'X'", only to then come face to face with someone very soon after and have to admit that I could probably never get along with that person unless all pretense were stripped away from us both.