First of all, yes, I'm aware of this argument. And I actually linked to it in the piece - linked specifically to Kevin Drum's piece in Mother Jones (which is really a must read) on the question, which is the best I've found in the popular press.
Basically, I don't think this question is settled, though I'd say that it seems highly likely that lead played a significant part in the growth of violent crime in the US in the second half of the 20th century. I'd even go further to say that it's the only theory out there that has any rigorous or statistical basis at all. Changes in police strategy, the rise of abortion, greater incarceration rates and a bunch of others are more or less just asserted and backed up by loose arguments about correlation. Police strategy and imprisonment probably played some role - just because how could they not have basically. But in any sort of rigorous sense there's little to no evidence behind them.
One point to note is that there's no lead abatement lobby. Cops, prison industry folks, various political lobbies all have reasons to push their argument. So they get more play.
Lead on the other hand has two big evidentiary chains behind it. One is the abundant evidence that lead poisoning early causes decreased IQs, diminished impulse control and various sorts of sociopathic behavior. It seems to take the 'natural' aggressive impulses of young men and put them into overdrive. Second is the very granular correlation between rising and falling rates of lead poisoning and rates of violent crime - offset by about 23 years. This doesn't seem to apply just broadly in the USA but in other countries and even state by state in the USA.
That's serious evidentiary backing. And I'd call it a solid theory. I just don't believe it's case closed. I think we need more research and also we'll need to see what happens over the next ten to twenty years. More candidly, I think there's part of me - perhaps the historian part of me - that's inherently resistant to such monocausal explanations. But that may be bias more than clear thinking.
So that's where I come down on this. Lead's the only theory with solid evidentiary backing. But I don't think it's case closed.