But don't you see that opiates only make people do these horrible things because they're banned!? Opiates don't turn people into devastatingly manipulative thieves, they turn them into people who will do anything to get opiates. If you changed two things, junkies would be no more likely to engage in destructive behaviors like theft than alcholic or smokers. Those two things are making opiates cheap and easy to get (regulate them like cigarettes, say), and eliminating the employment stigma. Opiates aren't great for productivity, but they are much less of an impairment than alcohol, and alcoholics are almost always functional unless they also suffer mental health issues. Opiates slow down thoughts and movements somewhat, and they make you feel really good, but they don't make you stupid or rash like alcohol.

That's not to say that there wouldn't be problems with opiates. You'd probably have as many people on opiates on the road as we currently have drunk drivers (again, they probably wouldn't be as bad, because while opiates slow reaction times and reduce alertness, they don't make the user think they can do things they can't). And junkies would probably still squander their potential to an extent, and mothers of brilliant children who take up opiates instead of going to college might be devastated. But I think most of the new addicts that would be created by legalization would be people who would otherwise become alcoholics, people just looking for an escape, and society prefering clean opiates over alcohol would do wonders for public health.