The most evil is outlawing those street-drugs, and then selling those street drugs as you are the biggest, baddest gang on the block. Now, that is evil.

Now, about their use, it has a horrible effect on the society.
What they do to themselves isn't my concern. But they so often cause a lot of hardship on the people around them.

Our justice system works on money (works for the banks), so how do you apply a penalty on the drug users for their destruction of the society? Almost all of them are losers without a penny to their names. (Loser, meet drugs. Drugs, meet loser) And so you can't get them to pay for the damage they cause.

So, we did the only thing left. We criminalize the activity.

A real solution is to never let a person consume Tell-lie-vision.
Get rid of govern-cement schools that separate kids into good kids and losers.
Actually have a society that cares about its people.
Do not let develop in a person the soul sucking desire to just check out.

And, have a way to kick a person out of the society.
(If, after all attempts at intervention, they still want to continue with drugs, they can do so over there, away from the people of society (out in the wilderness))