Pretty sure this has been posted before, but really just confirms what I've always thought. Exposure to other people, cultures, beliefs is what cuts down on racism, xenophobia, hatred, etc. and when you are a fan of an athlete with a different background as you, you are a lot less likely to view that background in a hateful way. I doubt kids that grew up idolizing Michael Jordan became racists against black people as they got older.
It's much less that these fans/people are good and those fans/people are bad. Everyone has good and bad in them, and the more positive exposure individuals get, the more the good will come out.