The dogma survives because it is politically useful, not because it has met any test of facts. Innumerable facts against it can be found around the world and down through history.
All sorts of groups in all sorts of countries have been demonstrably better than other groups at particular things, whether economic, intellectual, political or military. This fact is so blatant that only people with great cleverness can manage to deny the obvious. That cleverness is what creates the tangled web of confusion that has plagued civil right cases for decades.
Does anybody seriously doubt that blacks usually play basketball better than whites? Does anybody seriously doubt that the leading cameras and lenses in world have long been produced by Germans and Japanese? Or that Jews have been over-represented among the top performers in various intellectual fields?
Many groups whose performances have greatly outstripped the performances of others in a particular field have often been in no position to discriminate, even when the disparities have been far greater than those between blacks and whites in the United States.
In a number of countries, powerless minorities have so outperformed the dominant majority that group preferences and quotas have been instituted to favor the majority group that has otherwise been unable to compete. This has happened in Malaysia, Sri Lanka, Nigeria, and Fiji, among other places. Before World War II, quotas to benefit the majority were common in a number of European universities, where Jewish students outperformed others.
It is not stupidity, but ideology and politics, which allow the "disparate impact" dogma to create a tangled web of deception in even the highest levels of our legal system. The recent Supreme Court's decision in the New Haven firefighters' case was a rare example of sanity prevailing, even if only by a vote of 5 to 4.