I agree with you, but in reality, a large enough company could face (and lose) a wrongful termination lawsuit if they do this too often. The burden of proof for this is surprisingly low and engineering pays well enough that many of them can afford good lawyers.

Plus there's the added risk of hiring "duds" that are also minorities. And letting too many of them go will make it look like formal discrimination. Which is a much, much more expensive mess.

And then there's this issue of finding the duds. Easy for the people on the ground to spot, but less so for management and HR, which will require some form of reasonably accurate performance evaluations.