"By this reading, we're expected to accept that a little bit of Jeremiah
-- who thinks the government invented the AIDS virus, that 9/11 was a
homegrown catastrophe -- resides in anyone made to ride in the back of
a bus"

I think that's an accurate description of Obama's point, and I also think it happens to be true.  The point is not that the experience of discrimination will force people to think in particular ways--human beings have an amazing ability to think for themselves and transcend their background and experience.  But it would be completely naive to think that we our history does not exert a pull on our psyche in one way or another--that we aren't influenced by internal "little Jeremiahs" or "little Ferraros.".  In my experience, people who experience severe discrimination, poverty, or suffering--no matter their race--tend to view the world suspiciously and are prone to paranoid conspiracy theories.  

What Obama is saying is that we can dismiss the conspiracy theories for what they are, but that we shouldn't dismiss the people who hold those views, because their complaints are legitimate even if their philosophies are insane.

--Z