Step 1: HUD files a complaint against Facebook for allowing ad targeting based on certain criteria.
Step 2: Facebook bans advertising targeting based on the criteria in the HUD complaint.
Step 3: Advertisers react by targeting based on demographic correlates of the categories from step #1.
Step 4: HUD notices that ads are still getting delivered more to one group than another.
GOTO STEP #1.
There's no clear point at which this process stops. Demographic correlates are numerous and strong. Are you going to ban all of them? That's tantamount to banning ad targeting generally!