I mean, that's a deep philosophical question that depends on how libertarian you lean, how rational you think we are as humans, and whether people have access t

I mean, that's a deep philosophical question that depends on how libertarian you lean, how rational you think we are as humans, and whether people have access to perfect information. There are plenty of "voluntary transactions" that society has found necessary to either ban or at least regulate. High-interest loans are regulated in many countries, precisely because they can be predatory, but so are things like drugs. Even legal drugs are pretty heavily regulated for many reasons, including making sure consumers are aware of both the benefit and harm/side-effects that can occur.