The outcomes from legalization/decriminalization of any drug is increased use. This happened when prohibition was repealed. Drinking and death from cirrhosis went up. However, violence went down. So, there is a choice.
People will not always do what is in their best interests. That is a fact of life. So policy makers can either deal with this fact, and enact laws like they have in Portugal, where all drugs have been decriminalized (not legalized) and the savings is put into treatment, or policy makers can punish users.
Either way, recreational drugs exist, and they exact a cost on society. So we can either deal with the cost, or wish it away by saying, "you shouldn't do that".
If heroin were made legal, I wouldn't start using it, and neither would you. In fact most people wouldn't. Nor would they start smoking weed. Just as they do not pour vodka in their morning coffee. Some people, however, will. And that is just a fact of life, which we all have to deal with and pay for, one way or another.