Couple of points.
1 Nobody is saying that Semenya is not a woman. What they're saying is that she benefits from having some aspects of male biology. We don't exactly how much this amounts to but the best bet is that she has internal testicles that are producing an amount of testosterone close to the normal male levels.
2 To call this a racist decision is nonsense. The IAAF regulations were drafted under the leadership of Papa Diack of the Ivory Coast and are a lot less tough than they were in the past. I can give you the names of British, American, Italian, Dutch, Indian, Romanian, Austrian, Russia, Spanish athletes whose careers were ended before they achieved anything near what Semenya has won. Anyway, if Semenya gets banned, it's highly likely another African emerges to take over from her.