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.
These are all fairly strongly regulated. Did you choose bad examples on purpose?
So like,what about making gambling work like credit cards: you get a license that allocates a monthly cap based on a combination of credit score and income. It starts very low and scales up to, I don't know, 10% of income?
We should be free to ruin ourselves if we so wish, but if we are set on a track like that, others should be made aware so they can react as they wish.
Same with drugs, if you get a drug use license, then employers can deny you jobs, you may not be allowed to drive, be trusted with loans,etc..
You get rights, but they come with responsibilities and restrictions.