I think you guys are vastly overestimating the competence of the average doctor. I'd feel safer with most of the experienced BLers shooting me up with heroin before letting some random doctor do it.
To be honest, I can kind of sympathize with him, not so much on the dose thing, but how many times have you had the discussion with a non-drug user (usually a partner or family member) who says 'well why can't you just stop doing it?' Because of course someone who's never tried a drug like heroin would never understand the seductive allure it holds. I don't think he was intentionally trying to 'get his wife addicted,' that seems like a bit of creative journalism to me. Nobody intends to get themselves addicted, let alone anyone else. I'd say he was probably fairly new to heroin use and in denial about his relationship with the drug. When his wife called him on it, he said 'no, you just don't understand why it's so wonderful and it makes me happy and I feel like a better person on it and I'm not really addicted anyway I just do it to relax after work etc etc,' talks the wife into trying it in an attempt to help her understand why he's so attached to the drug, then through plain old carelessness (or maybe an unusual batch) he accidentally doses her too highly and she OD's.
It's tragic, and a doctor really 'should' know better, but the sad truth is that they quite often don't. A lot of doctors are really very naive when it comes to recreational/street drugs.