I don't disagree with you there. Some of these things are perniciously difficult to substantiate. However, in the case you just mentioned, I think you did a decent job of substantiating it. George Bush is indeed contrary evidence to the assertion that people don't hire blacks due to inarticulateness.

Some things for sure are really difficult to substantiate though. But what is the alternative? Ultimately, to enact change, you need to convince some portion of the culture that it's the right thing to do, or that there's a problem in the first place. I think there's a lot of evidence that efforts like that have been successful over the long term in a number of different areas.