Earlier quoted context omitted.
The flaw here is in expecting Facebook to be the police. Here's what happens if you make Facebook do it. They become aware of someone running an illegal ad and ban them. But the advertiser is a criminal and still wants to make money, so they make a new account or find some way to avoid detection, and the ad ends up back in the system, and the advertiser can do this forever because they're making a net profit by conti…
Since ads are targeted, only Facebook can know when an illegal ad is run. Are you suggesting Facebook should be reporting the people running ads to law enforcement?
In general, they should not impede investigations, and not intently help criminals.