your assumption regarding desegregation leading to a reduction in mistrust and potential for violent conflict is unprovable.
isolationism was a strong current in America prior to the First World War, and even extending into the second. Japan spent centuries enclosed within its borders, China too. Hinduism created the intellectual framework for a harmonious and insular (and inward focussed) Bharat too.
these are cultures and peoples who had strong identities and did not seek to mix with other identities, they were neither threatened nor a threat. compare that to the present day... all pervasive Corporate attempt at homogenisation of humanity into cultureless sludge.
people are more at odds, more willing to go to war, weak in response to despotic leaders (Blair, Bush and other similar war criminals).
people also actually loathe each other more, it would seem, if you judge by how apathetic we are politically. since politics is social action and responsibility and a lack of inclination to be responsible for your fellow man is a good indicator of a lack of esteem for him.
racism is not "wrong", that's a perversion of morality to apply it to such a thing as racial awareness and preference. instead you can say that it has disfavourable outcomes - too narrow a self-image prevents one from wanting to unite the world under a common flag etc, lack of willingness to adapt to the latest fads, leading to a sense of listlessness and alienation from society at large ... but "wrong" would assume that in and of itself it is harmful, it is not.
another point, violence and dislike are innate parts of human society, they will never be removed from society, but racial identity and grouping actually might prevent a lot of people from internalising those feelings and instead standing strong and benefitting their own communities, under the feeling of self-worth and cultural pride ... objectively that can't be a bad thing, can it?