Don't fall into the trap of "everything not mandatory is prohibited".

Google doesn't really want scam ads. It doesn't make a lot of sense to penalize them for removing some of them just because their process isn't perfect; removing them doesn't have to be banned.

But if you make not removing them mandatory, you're replacing the justice system with a private corporation, which is pretty crazy. If the police accuse you of a crime, they have to prove it to a judge and jury. You can appeal to a higher court. Google doesn't have that. And if you add liability for not removing something, they're going to err on the side of removing things they ought not to, with no recourse for the victims. Competitor wants you out of the search results? Report it to Google and you're out, because they get a billion complaints and removing them by default is safer than getting prosecuted for missing a real one.

The correct solution is to let Google remove things that are bad without punishing them for not being perfect -- maybe even err on the side of imposing (civil) liability for removing things they shouldn't instead of not removing things they should -- and rely on the criminal justice system for going after the criminals.