*IF* it were true that black people were dumber on average...?

I would say it's always wrong to make umptions about somebody based on their race. Even if a study proved 99%+ of a race developed less higher thinking processes than other races. Who's to say you're talking to the 1% that's not? Although most people will make umptions based on previous experience or what studies find/the media tells them. As for hiring black people, you should hire them IF they're the best person for the job, which is what interviews/trial periods are for.