The majority of black democrats don't even know why they vote democrat other than because they're black & someone, usually their parents...told them republicans are racist. That's really all there is to it, in most cases. Atleast that is my experience. Others like Asclepia's atleast have some curiosity and educate themselves on it, but they never(Im not saying Asclepias doesn't)question their sources & do cross referencing to see if what they were told is correct. They get told to be a democrat, then they go to democrat & liberal sources, those sources tell them republicans are racist, and bam! There you go, mind's closed. I doubt this is limited to black folks, Jews tend to be the same way. They treat politics like it's a family tradition instead of being objective about the issues of the day & which policies will actually benefit them. Liberal Talking points rule their decisions.
Even most white Democrat voters usually don't know why they're democrats other than "My dad was in the union, union supports democrats".
It happens with people who vote republican too, though on a much smalle scale.
That's because the republican voters tend to fall into a few different strains of conservatism. You have Paleocons, Tradcons, Libertarians, Neocons, Tea Party recently.
These groups only agree to a certain point & then split. Liberals are just that. Progresive, liberal, same thing. There is no serious disagreements in the Democrat Party, they're pretty uniform on the issues that matter.
That is why I predict you'll see a small but steady stream of blacks leaving the Dems...especially if they're church going blacks in the south.
I'd rather they become Libertarians because we could use the help & also because I believe that's where black folks would fit in the most today.