My suspicion is that the real deep down cause for a lot of white writers sticking to white characters is not so much 'if I try and write not-white characters I will end up being a little bit racist and I might offend people so I better not try' but more along the lines of 'if I try and write not-white characters I will end up being a little bit racist and will be smacked down severely for it and so it is much safer for me not to try.'

I am not saying that this will or won't happen, but I do think the reasoning is more fear based than 'thinking of other peoples feelings' based.