I'll happily change my mind in the face of evidence. Usually I see a lot of hand-wringing and speculating about it, rather than anecdotes and data. Proving causality in some kind of observational data set might be difficult, but I am not one to discount individual people's experiences either.

So if you have examples of unqualified candidates being hired on diversity grounds, then I'd like to hear your stories. In my own professional and social circles, it's very rare to see an unqualified hire at all, so maybe my personal sample isn't where the problem happens.