I don't think anyone is defending racism, just pointing out that all demographics voted leave, remain, it's not clear cut poor people voting leave, comfortable, well off people voting remain, white, black, asian picking remain or leave. Immigration fears, racism was a huge part, no doubt about it and the leave campaigns, media played it like a fiddle and the resulting leave win only encouraged racists which is a terrible outcome but one that probably needed to show it's head that it's here and will always be unfortuately, needs called out and fought against. I would also say it's not always white on black or asian hate, it does happen the other way, the fear of the other, EU immigration crossed demographics too.
As for other reasons, sure people just don't like EU, believe it's a waste of money, believe all the lies over the years or maybe legitimently think we can go alone even if they are wrong or right, these people may be few and far between and it's just cover for fear of immigration, society changing, quite possible but let's not forget 70% voted in the election, 33 million people and 17 million voted leave in a country of 70 million. Hate is everywhere but I'm trying to be positive and hope we turn a corner and people see the good path now and the obvious lies.