"Is it even possible to be a responsible Heroin user?"Many years ago I read of a long-term study which followed heroin addicted doctors for 20 years, in a society which guaranteed them a supply of clean heroin, and found that as long as their supply was clean and uninterrupted these heroin addicted doctors actually performed slightly better than their non-addicted colleagues, and there were minimal if any negative health consequences.
Unfortunately, I haven't been able to find the study since[1], so take that with a grain of salt.. and heroin is not really my subject of interest so take the following with another grain of salt, but my impression has been that pure heroin is actually not that harmful, especially compared to something like alcohol or cigarettes.
The main problem is the potential for unintentional overdose, which really shouldn't be much of a problem with pure heroin (or not much more than many other prescription drugs, whose use doesn't have any negative moral stigma attached to them). If people know the purity and dosage of the drug they're taking they tend not to take so much that it would kill them... not accidentally anyway. It happens, but it also happens plenty of other prescription drugs.
There's also addiction, but if you can get a pure, cheap supply (which should be the case where heroin is legal) and it doesn't cause any serious health consequences, then what's the problem?
[1] - If anyone else can find this study, I'd be eternally grateful.