That's a good question and a correct perspective for arguing these kinds of policies. The answer is "as far as possible".
Personal freedom should be default starting position. If it is going to be taken away it should be done in a way that is as minimal as possible while getting the best bang for the buck in terms of minimizing actual harm (with actual evidence backing it up).
"I don't like other people doing drugs, so we should put them in jail for that" does not meet this standard (or any standard worthy of it's name, to be frank).
"People will harm themselves by doing drugs so we will ruin their lives and put them in jail while spending way more money than it would take to actually help them" also doesn't meet this standard.
What makes a drug addictive is not the substance itself, but the environment which surrounds the 'addict'. An environment that is poor in social connections and purpose makes drugs more addictive to the users.
Drug use is still illegal. The difference is that you won't face justice and you won't go to prison. Instead, you will face a commission and they may send you to a rehabilitation center, or fine you for a reasonable amount.
Drug trafficking is still a crime which carries heavy penalties.
Yes, and then use the massive amount of money that goes to militarizing police and incarcerating none violent drug offenders for public health services such as counselors, rehabilitation, safe usage areas, HIV/hep testing, etc
Interesting line of thought, but how far do you take it? Legalize all drugs, even the ones that may end up killing people, or make them completely dependent?
A society that values Freedom needs to ensure its people remain free, and there are clearly substances out there that can make you a slave. How do you deal with that?