My philosophy on the broad subject:
I think many people have strong gut reactions on encountering certain people who are different to them - a pure animalistic response; an Other who My People should be protected from; I think there's a stage where it's a pure emotional response without any justifiable foundation.
The problems - racism, sexism, homophobia, anything like that - come from people who seek to justify that emotional response in itself, rather than recognising it for what it is and permitting your brain to overrule it.
(I think this stretches further when you couch it in terms of 'challenging a belief', too; the same principle applies; many people will place more faith in a belief - because if they genuinely wholeheartedly believe it they can't countenance that belief being incorrect - than in the rational explanation of what they're encountering)