There's absolutely nothing inherently wrong with heroin if it's used in a reasonable manner for something it can actually help with. It is, in fact, quite useful to deal with some kinds of physical pain. It's been eclipsed in recent decades by other kinds of opioids, but that's a difference of degree, not kind. Heroin isn't magically evil just because it's become a bogeyman 'substance of abuse' over the past few decades.
The point is that drugs are not inherently evil. Some drugs might be more harmful than beneficial, but that can only be determined by trials and evidence. Demonizing the things is the exact opposite of helpful.
In fact, I'll amplify the point: Injecting morality into things without a moral dimension is very harmful. It prevents people from looking at things rationally, by clouding the issue with emotional noise.