Found this tidbit over on Reason TV, in which a Professional shrink has researched psychopathic murderers, and discovered some common characteristics:
He also notes that libertarian folks, even with two out of three of the flags, don't become serial-type murderers, even though the temptations are certainly there.
I note that the average gun owner tends to be quite conservative, with a libertarian streak.
I also note that the average serial killer seems to be a liberal with a strong sense of entitlement, and frustration at not getting his due.
Disclosure: D'wife is a psychology major. From observing her coursework, I have concluded that psychology is what the application of statistics can do for ordinary witch doctory, and that anything coming from the field should be approached with the sort of caution usually reserved for venomous snakes and alligators.
Still, the argument is as valid as anything the antis have come up with, and Mr. Fallon obviously needs to do more research (job security). Going to the Dean of a liberal (U.C. Irvine) university and asking for funding and tenure to study why liberals are inherently psychopathic mass murderers, and Republicans are the only people who can actually be trusted with firearms might be a hard sell. Some thought obviously needs to go into the wording of the title on the fund request.