It's worth noting that the original Title VII of the Civil Rights Act of 1964 did not cover state and local governments, and required amendment in 1972 after Congress found that police and fire departments remained highly segregated. Likewise, the law signed by Lyndon Johnson did not mention "disparate impact", and it was not until the mid-70s that Congress followed the Warren Court's innovations on this front. If employment discrimination laws from the 1960s still existed today, the city New Haven wouldn't have thrown out the results of theor promotion exam, since there would have been no grounds for a lawsuit to dispute an exam that was in theory race-neutral but discriminatory in practice.
This is the sort of story that makes me think Ezra is right to critique the Big Bang Theory of Legislation. Once the political establishment agrees that something is a problem, the tendency is improve on existing legislation rather than unroll it entirely. To wit, while George W. Bush engaged in some rollback of environmental regulation, he was unable to fully unwind everything accomplished by Bill Clinton, meaning that the current state of environmental regulation is somewhat to the left of where they were when Ronald Reagan took office (and, it should be noted, George H.W. Bush signed amendments to strengthen the Clean Air and Clear Water Acts). And under Obama they will probably shift leftward again. Sure, Waxman-Markey has lots of problems, but once it's passed, Congress will take another bite at the apple, probably within a decade.