Cato libertarians are ferociously ignorant about all things foreign-policy-related, ignorant not in the sense of being unaware of facts but of refusing to be influenced by them, and their views are written off by serious people.
Will Wilkinson of Cato answered:
I don't pretend to have any expertise in foreign or military policy, which was not in any case what my post about GDP as a proxy for welfare was about. Anyway, my Cato colleagues Malou Innocent, Justin Logan, and Chris Preble (among others) are some of the most best foreign policy minds in Washington, and "serious people" certainly do take them seriously. I encourage you to read their work some time.
I don't pretend to have expertise in foreign or military policy: I do have expertise. And I agree with Will. Some of the finest work on foreign policy in the last twenty years or so has come out of Cato's shop. Ted Galen Carpenter has done first-rate work, as has Doug Bandow, and now the younger generation is following their lead. Chris Preble has an excellent recently-published book on foreign policy that I highly recommend. If you want to see why, read my review.