Because like it or not, we still live in highly volatile, dangerous political times, and scientists getting behind the idea that there are clear racial lines dividing us all will not contribute to the peace-making. Its an uncomfortable truth that sometimes science is really hindered by politics, and this is one of those situations where its a highly, highly charged subject with potential to create a significant degree of upset in the world. The human species is very rarely actually prepared for the truths of science.