How about: it’s the responsibility of people posting ads on Facebook to follow the laws that apply to them.

I don’t see why it’s Facebook’s responsibility to police advertising for housing and control how it’s targeted. If advertisers use illegal targeting then that should be on them.

Why does it always have to be either-or. Can't we all agree that Facebook also has some responsibility to prevent abuse? I'm not saying they have to make sure no one can ever break a law using their platform. But once they become aware people are abusing it to do so, how can you say it's fine for them to ignore it. This seems to be the case, as far as i understand that filing. That's how you end with government having to impose regulation. I'd prefer Facebook willingly work with law enforcement or/and their clients to make sure forced intervention won't be necessary.

Exactly, whichever is most effective. The aim of the law is primarily to protect against descrimination, not to blame a certain party. Both the publishers and the buyers are at fault but whichever changes get the problem fixed seems the best way to go.

Getting Facebook to disable some targeting option seems like a much easier route than going after each ad buyer. Targeting the publisher makes sense because they are in the best position to enforce policies on their platform and stop the descriminatory practice at a larger scale.

The people publishing these ads are literally paying Facebook to do so. IANAL but as far as I know it's not legal to profit off illegal activity. Facebook are, themselves, breaking the law here.

What law specifically makes it illegal "to profit off illegal activity"?

That sounds incredibly broad and impossible to to avoid.

I imagine you'd be considered an accessory to the act in question. There are also laws like this [1], although they don't apply to this situation.

[1] https://en.wikipedia.org/wiki/Son_of_Sam_law