To add to what Kevin wrote below, David Frum offers to debunk three myths about 9/11 and I think he goes two for three.
I think Frum is correct to argue that the notion that poverty causes terrorism, in addition to the idea that we can't fight terrorism without first solving the Israeli-Palestinian conflict, are myths. It's his third myth, as Kevin notes, that goes horribly off the rails. In Frum's reading, it was a myth that "invading Iraq will lead to a surge of Islamic terrorism worldwide."
But it's not a myth - it's what happened. In 2003, 2004, 2005, and 2006 there was a sharp increase in terrorist attacks - both inside Iraq and around the world. In 2007 and 2008 those numbers fell, but they were still way above the pre-Iraq war levels.
Frum later tries to caveat his way out of this obvious error by insisting that there wasn't a "surge in rage" against governments that supported the U.S.-led invasion, but this is also wrong. The intelligence services of several allied countries (and the United States' own intelligence agencies) have insisted that the invasion of Iraq was a radicalizing event. And then there was, you know, actual terrorism directed at these governments, including the 7/7 Tube bombings in Britain and the Madrid train bombing in Spain. Neither of which are mentioned by Frum while debunking this "myth."
I would suggest that Frum swap out this erroneous myth with a cherished shibboleth from the neoconservative canon: that democracy is an antidote to terrorism. As we've seen in the profile of recent jihadist arrests, being born and raised in a democratic society does not seem to have any bearing on one's propensity to take up arms against the West.