I struggle a lot with the potentially nonzero overlap between
a) "just legislate that being racist/sexist to people is illegal, then have judges interpret" (which is what seems to be simply necessary to actually make progress against the endlessly inventive evil of racism/sexism),
and b) "but also don't simply make everything illegal because then abusers can selectively enforce the law to punish groups they dislike".
Tough. Gotta try, though.
I think a) seems very quixotic and causes more problems than it solves.
Instead, I would say that discrimination should probably only be illegal in places where there aren’t enough of the thing (jobs, etc). For example, what about x-only clubs, or ladies’ nights or gyms or etc.
Evaluating a policy based on Disparate Impact is important because it gets rid of the truck-sized plausible deniability of "Well, see, our policies aren't technically racist, even though the end result is clearly that racial minorities are excluded/avoided/attacked/whatever. But since we don't specifically and consciously mention race, then we're in the clear!"
It's kind of a corollary to "The Purpose Of A System Is What It Does": The purpose of a policy is who it impacts. Disparate Impact recognizes this.