It makes no sense, it is the person's money and life, and it is theirs to ruin as they wish. We are not properties of the state. If a person cannot be allowed to do what they wish with their own money, because they might harm themselves or others as a result, then how can you trust them with driving a vehicle, flying a plane, operating weapons in the military, or even owning a personal weapon?
Every gun sold to a person is a gamble on whether they use it to cause harm on others (same with the things i listed above).
This same logic applies to regulation of drugs in general as well in my opinion. Regulating other peoples lives is not the purpose of the government, especially when they're not harming others or being a nuisance to the public.
3 of these require significant training or at least licensing and the last one is banned in the majority of western nations.
I'm with you that personal responsibility and freedom should be the norm, but active predators (Drug dealers, bookies, social media companies) should probably have limits put on what they're allowed to do.
For your last statement, I agree, "active predators" should be restricted or punished because their intent is to cause harm at the cost of others for profit. but if they're just selling the "drug", why should that be restricted? You can force them to inform their customers of the harm,but that's about it.
This is the entire gambling industry! Do you think they don't know that their best customers are addicts who are blowing their kids' college fund?