You are telling me two guys from the same ethnicity or background don't make crude or crass jokes about others? Some may mean it, some may just do it for laughs but shit happens.
To a very, very small extent. The texts and emails they've released (there could be plenty more) go a bit further than that. They barely pass as 'jokes'.
I've got plenty of friends of all backgrounds and colours and of course, you can joke about racial stuff with them - but only if you know they're comfortable with it. But nothing to the extent of what has been released.
How could you possibly defend what Sterling said?