The 90's showed exactly what I, Papa and others have said - diversity is a weakness, not a strength. When people view themselves as different, they will in turn start to believe in quasi nationalism where they view themselves as superior and "why are we part of this nation if they are different from us". Chechnya did this and also committed atrocities that dwarf whatever happened in the US.
No, diversity doesn't work especially when you got cultures that contradict your own and own laws. As well, as long as human greed and stupidity exists, so will the ideas of racism will too. And no, many cultural groups are far more racist than average whites and I see this every day where I am in a diverse country. Vietnam, where you are from isn't a diverse country. So you don't get to state what works and what doesn't when;
1) USSR failure and events shortly after proved me correct
2) I am in a diverse country of Canada which I see racism live and well in the minority groups and trying to all strip rights of others away to push the crap they left their country for, here.
So spare me your lack of knowledge and experience in this