I think everyone's racist on some level whether they admit it or not (it could be said that the title of your post is racist).
But to get to the main point of your question, as a white person looking at the world I see (or get the impression) that most of the countries which are primarily populated by black people are problematic. Whether that's in terms of bad governance, low productivity, high crime rates or all three. On this point, if you're looking for the main cause of racism I think it is probably Africa. A continent with likely more natural resources than anywhere else in the world but it just can't get its **** together - no matter how much help, and how many billions of dollars are poured into it. Even South Africa, which should be an example to the rest of the continent, is a joke. What does a government like that say about Africa to the rest of the world?
The second point is that that wherever large populations of black people settle in the world, these areas seem to become as problematic as the countries from which they originate - high crime rates, etc. You can call up whatever sociological reasons are behind this, but the bottom line is that no one cares if a group of Japanese people or German people move into the neighbourhood, and there has to be a reason behind that (not 'racism', but what underpins it).
People can't talk about racism honestly, so the debate is always clouded. It must be horrible to be a decent, hard-working black person and face discrimination, but people aren't racist for fun, there's a natural, human thought process behind it. However unfair or unpleasant it is.
The above is just my half-baked opinion, a point of view which hopefully provides a some insight. I've always thought that racism should be defined by whether or not you (for whatever reason) hate an entire race of people. In my opinion only a moron would hate an entire race of people but races are different,they have different characteristics, however much the liberal world would like to prove that we're all exactly the same. I think that until people admit to that the debate is pointless.
Finally, I'd just like to highlight, in case it's not obvious, that's it's not my intention to cause hurt or offence with what I've written.