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.
You don't deserve any rights or liberties if you can't accept the rights of the drug addicts,gamblers, homeless people and many more types of people out there.
It is a fundamental aspect of the human experience to self-determine one's fate.
It is unfair and unjust to punish someone based on probabilities. A innocent person should not be treated like a criminal. A free person shouldn't be treated like a prisoner or a slave.
The government has no authority to punish citizens because they might commit a crime. Citizens are subject to the rule of law. But in exchange for compliance to the laws, we expect a fair and just treatment under that law. That is the contract.