It's not consenting adults if it's a scam, and Google can't analyze every ad to check for that. In a space where most ads are scams, this looks legit to me.
If you're serious: you're welcome of course to an opinion that google is right to block scams, and / or that most cryptocurrency ads are scams.
But you can't really believe that adults stop being adults, or that consent to judge the merits of, for example an ad, suddenly evaporates in the presence of a scam?
Is the presence of a scam sufficient to warrant treatment of the involved individuals like children?
Scam = based on lies. EG I tell you that your money will be used to do X, while instead I use it to buy a new home for myself. If one is lying, the others aren't "consenting".
I think I'm reasonably capable of giving consent to a situation wherein I know I'll need to discern truth from lies. I mean, I understand there's a limit to human agency, but the mere presence of a scam in a google add isn't close to it, at least for my worldview.
It's their business, they should be allowed to decide whatever they want.
In the same way we can think that most of the businesses are scams, because most of them end up bankrupt after 5 years. Should they also ban the ads for products of companies younger than 5 years? To protect the consumers from becoming bag holders of unsupported and unusable products?