The only viable solution is #4. So long as Facebook can make money by targeting specific groups or behavioral features, their algorithms and advertisers will find facsimiles for protected groups, the vulnerable, children, or Nazis since this optimizes revenue and engagement in dramatic ways. Even the most well-intentioned actor -- and Facebook is very far from that -- could not win this self-imposed game a whack-a-mole.
One alternative to shutting off targeting altogether would be switching from a blacklist to a whitelist approach, where regulators provide the set of features or groups that are allowed to be targeted.
One alternative to shutting off targeting altogether would be switching from a blacklist to a whitelist approach, where regulators provide the set of features or groups that are allowed to be targeted.