Pretty much everyone I know including myself have something kinda like this junkie code you describe. Essentially just a mental rule that we won't be responsible for someone's first experience with heroin. Once they've tried it, it's different. But even if a lot of us still really enjoy heroin even for all the pain it's caused, I think a lot of us, and certainly for myself, already feel a lot of guilt for shitty things we've done without the added guilt of possibly starting someone else's habit.
Nobody I know is willing to knowingly be responsible for helping someone try heroin for the first time. I have a friend who realized that someone had told him he'd used before, but when the time came it became obvious that he really hadn't. Since the drugs belonged to him (my friend) , he put a stop to it and wouldn't let him (the guy who lied and really hadn't used H before) use it. Not for the first time, not with his drugs.
I dunno what this is like for guys, but one difference might be that women are more likely to be offered sexual favors in exchange for drugs. I've gotten those offers lots of times.so, if you're a junkie, and female, chances are even if you never seek it out, sooner or later you'll be sick and desperate and someone will make the offer.
Which is part of why I think the stats for female heroin addicts that have sold themselves at least once at some point are likely very high. That and the fact that just the ones I know personally is pretty high and there could well be some that just can't bring themselves to admit it
