Since you specifically requested my argument...
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.