from what I've observed across many fantasy universes, acceptance, kindness and tolerance are not generally widespread in most universes. this is because most fantasy universes want combat and you can't really have that if everyone just accepts everyone else, unless you go for an anime style tournament and competition set up. but....well not everyone likes that set up. not for everything.
The kindness/acceptance ideals not being a big thing in fantasy holds true across DnD, WoW, WH40k, Exalted, Game of Thrones, Lord of the Rings, Wheel of Time, and so on. and thats not even counting the monstrous always chaotic evil races, because elves hate dwarves and dwarves hate elves. Elder Scrolls has it own share of racism even if it is or was mostly conquered by one empire. things like that.
Mt:G isn't really different in that regard. its prejudices are just divided along philosophical lines rather than cultural or racial ones, though you can argue that what mana colors someone holds to is often their culture.
Personally I think all MtG colors have the potential for acceptance and kindness, even Black. White and Green are obvious, Red's emotions allow it to empathize, Blue can think through anothers viewpoint, and Black in my opinion is not above recognizing that accepting others and being kind can be beneficial to themselves, nor does Black mana really care what you are- anyone can be powerful, anyone can work towards their own gain, they just have to seize it, and the reason why they want to use this power doesn't matter. I'd even say that individual rights and liberties is an inherently Black mana philosophy rather than White mana philosophy. Black mana is also the will to survive, a trait it shares with green mana.
you may disagree, but I don't care. its not my place to tell anyone what to believe. only what I personally believe that is intuitive to me. though as I am Blue/red/black I have a bias against white/green.