Heroin is pretty awesome though

Naw. I'm sticking with "nut job". First and foremost, ANYONE who even TRIES heroin could most definitely be considered a nut job. It never ends well.
I'm very familiar with opiates and have seen their devastation, up close and personal in a close family member. You are correct. In their pure form, opiates are non toxic but VERY few addicts have access to anything even remotely pure. Street heroin is a total crapshoot and calling that more "safe" is like saying a revolver with one bullet in it is safer than one with two, when playing Russian Roulette!
The risks of heroin and other opiates reside almost completely in either overdose (a danger of most substances) or non-sterile use of needles/complications arising from that route of administration, as opposed to something intrinsic to the substance itself.
You left out the VERY dangerous, risky and unhealthy addict lifestyle. You know, prostitution, robbery, extortion, murder, suicide, bad drug deals, etc. Stuff like that.
Yep. Anyone willing to risk any of that? Nut job, for sure!
I don't love her.. She kicked me in the face!!

"Nut job"? How about "addict." All addicts are advocates of their particular poison. It's part of the disease. Also, Zoe wasn't using heroin when she died. She moved to Paris a few years before, and took up cocaine in place of heroin because the latter was so hard to find. She died of heart failure due to this extensive cocaine usage. (It's debatable whether she was much of a cocaine addict, though, so much as a heroin addict who used coke because it was the "best" drug available. Certainly she never seemed to advocate cocaine or other drugs in the way she advocated or praised heroin).
I'm not trying to minimize the risks of heroin addiction, but opiate use in and of itself doesn't damage the heart, brain, lungs, liver etc. like cocaine, amphetamines, alcohol or cigarettes do. The risks of heroin and other opiates reside almost completely in either overdose (a danger of most substances) or non-sterile use of needles/complications arising from that route of administration, as opposed to something intrinsic to the substance itself. This both makes opiates more "safe" and more insidious in their ability to addict, as one can use them for extended periods while still appearing/functioning quite normally, because the health effects are so much less burdensome than alcohol or meth, among others.

She was a total nut job!! Just like Layne Staley. Staunch advocates of what ultimately killed them both. SMH.
I don't love her.. She kicked me in the face!!

You know, I've read this and MOSTLY believe it
BUT I've NEVER seen an ACTOR portray being High the way Keitel did for this film. Maybe it's just a testament to his skill as a Method Actor but I must say, there are a few moments of questionable behavior. Maybe he took a tootski of Coke or Dope in those scenes because he shows multiple signs of being junked out

Harvey didn't use. Zoe Lund definitely did, though, as well as Ferrara and who knows who else behind the camera. In her scenes with him, Lund had to coach Harvey how to act properly "high." She gave him a saline shot, though she shot herself up with real heroin just moments before.