Actually, he says we understate the case, at least for the wars he mentions in a recent article Misallocated Infamy, about FDR's WW2 perfidy:
The late Murray Rothbard is said to have often argued that, far from being evidence of a “paranoid” strain in the American mind, belief in conspiracies as a factor in American history was usually not taken far enough. The truth behind most conspiracies, he alleged, was far more heinous and diabolical than even the most diehard conspiracy theorist suspected. The events leading up to the Day of Infamy in 1941 prove him right, no less than those preceding U.S. wars against Mexico, the Confederacy, Spain (1898), Serbia (1999), or Iraq (2003). In all of those cases diplomacy did not “fail” because it was not used to avert war, but to make certain its coming.
The article is excellent (as most of his usually are), and I highly recommend it.