I used to date a girl who said that she had used heroin in the past (not while we were dating). To me, it sounded like she was really depressed (and attempted suicide). She also said that the drug made her euphoric and felt very good while using it, but would not go back to that kind of life.
Mind you, she is one of the most intelligent, nicest and considerate people I've ever met. In fact, I would say that her previous experiences made her one of the most resilient woman I've ever seen. She works two jobs in a psychiatry lab, a bachelors degree from a top university, and is applying to medical school. So in her experience, people DO get off of it, though not 100% cleanly (most drug addicts will replace those harder drugs with 3 things: exercise, smoking and lots of sex [they give the brain a similar stimulation that heroin once gave them]. But in my opinion, probably better than depending on heroin).
My answer is no, we should not put people in prison for using heroin. My answer would be to help them get off the drug. Even if it is tough, punishing them would not help them get better. In fact, there are studies that show that punishing drug users would make them worse off and going cold turkey will make them have terrible withdrawals.
My argument is more pathos.
Now, let's consider that this girl I met was NOT resilient and motivated to be a "model citizen". Should we still put her in prison? After all, she is contributing to the illicit drug trade buy purchasing these substances. And under the influence, can attempt harm unto oneself (suicide). And they are knowingly doing illicit drugs and illegal activities (drug addicts tend to do more than one illegal activity). (That would be how I would argue with I were you!)
But If we put them in prison, do we expect to rehabilitate them? Or let them rot? It also depends what your values are, and what you want to do with these people if you DID put them in prison.
However, your husband's argument also states "we shouldn't imprison people....that do not have direct...effect on others"
Well in that case, smoking + 2nd hand smoking WOULD be a direct effect. Therefore, we should imprison them.
I see where your husband is going with it, but in context, drug addicts are not always low-lifes.
Anyway, I'd like to hear what ya'll think too! Great question.