As someone who is a good deal less supportive of an interventionist foreign policy than Phil but more of an interventionist than Daniel Larison, maybe I can stake out some middle ground. I’d say this: 9/11 was a good opportunity for a debate about what government is actually for. Conservatives, from Chronicles paleo to Commentary neo, have long believed that national defense is a more legitimate function of the federal government than, say, giving old people prescription drugs. A government that tries to do everything ultimately becomes less effective at the things it is really, constitutionally supposed to be doing.
This observation doesn’t solve all the problems of a neocon/libertarian fusionism. After all, there can still be disagreements about what constitutes a just national defense or vital national interest. Wars grow government, both in terms of foreign entaglements and domestic functions. But a conservatism based on performing government’s vital functions while shedding illegitimate or unsustainable commitments seems a lot more prudent — and thus more conservative — than one that fuses compassion at home with activism abroad.