I'd agree that lawbreaking is a reasonable moral choice, but not in this case. Moral lawbreaking, in my view, is done when there is a clear benefit or reason to the lawbreaking. And by clear I mean clear to a reasonable and moral person, and not just a speculative personal opinion.
Given that frame of reference, I would argue that (1) the notion that online drug dealing would lead to harm reduction for a drug addict is speculative rather than clear; (2) the harm caused by improved access to hard drugs by more potential addicts would be tremendous and therefore likely exceed any potential harm reduction; (3) given Ulbrict's apparent willingness to hire hitmen, I find it impossible to believe he was in any way motivated by concern for others.
That's fine; I disagree, but I'm not interested in litigating it here. But your original parent actually was arguing along those lines, cf. "rat poison" et cetera, so perhaps you'd like to retroactively not reject that as "not a reasonable argument".