There is a distinct difference between an identity that I have chosen based on my personal preferences and one that is forced upon me by circumstance. One I can change and has deep significance to me. One is assigned and immutable and has very little direct influence in my day to day life.

You have the strange notion that without nationalism to enforce an identity on myself that naturally there is no way my neighbor and me can live in "peace and harmony". I suggest that I can work with other people just fine, even if I don't share an identity with them. In fact, if you can only work peacefully with people similar to yourself I believe that is discrimination of some form or another. I realize no human is an ideal machine, but any person with empathy really ought to be able to work with women/men/muslims/jews/french/british/german/ginger/blond/tall/short/disabled people without issue - especially if they want to remain employed in the modern world.

Finally, please avoid insulting people who express a different opinion to your own.