I hear ya on like/dislike for Levy, but your statement about him 'veering' into legalization implies that it's unrelated, which isn't the case.
One of the underlying implications of his article is that gun-control advocates are not actually trying to reduce gun violence because if they were there are many other legislative dials that could be turned with far greater effect than banning a few models of firearms. And thereby he brings up drug legalization. IF one wanted to reduce violent crime in this country, and one knows that much of the violent crime in this country is a result of prohibition (who'd have seen that coming?) it stands to reason that ending prohibition - however that's best done - would cause a greater reduction in violent crime than gun bans. It's an example to prove a rhetorical point. I think his reasoning is sound regardless of one's personal views on the federal government's constitutional power to ban plants (or the wisdom of doing so).