Yesterday Jesse Walker noted David Frum's plea that we not let all the talk about gun control following the Tucson massacre distract us from the importance of drug control in preventing such horrible crimes. In a post headlined "Did Pot Trigger Giffords Shooting?," Frum wrote:

The Tucson shooting should remind us why we regulate [sic] marijuana.

Jared Lee Loughner, the man held as the Tucson shooter, has been described by those who know as a "pot smoking loner."

He had two encounters with the law, one for possession of drug paraphanalia [sic].

We are also learning that Loughner exhibited signs of severe mental illness, very likely schizophrenia.

The connection between marijuana and schizophrenia is both controversial and complicated. The raw association is strong:

  • Schizophrenics are twice as likely to smoke marijuana as non-schizophrenics.
  • People who smoke marijuana are twice as likely to develop schizophrenia as those who do not smoke.

But is correlation causation?

Frum then summarizes research suggesting that pot smoking hastens or aggravates symptoms in some schizophrenics. Since he has already diagnosed Loughner from a distance, he thinks it's pretty clear that the answer to his headline question is yes.

In other words, Frum says marijuana prohibition is necessary to prevent mass shootings like this one, which it manifestly failed to do. I guess he's suggesting such crimes would be more common if pot were legal, but he could be wrong about that: One possible explanation for the association Frum cites is that schizophrenics "self-medicate" with marijuana. Consistent with that theory, one of Loughner's closest friends told Mother Jones that "after Loughner apparently gave up drugs and booze, 'his theories got worse....After he quit, he was just off the wall.'" Maybe pot prevents more mass murders than it precipitates, in which case the Tucson shootings should remind us why we need to legalize marijuana. I wonder how Frum would react to that suggestion.

Wild speculation is fun (and versatile), but let's not lose sight of Frum's implicit premise that the government should strive to make the world as schizophrenic-safe as possible. If schizophrenics might react badly to something, Frum seems to think, that possibly bad influence should be banned. Sound familiar? More on this sort of reasoning in my column tomorrow.