As a good libertarian, I'm pretty skeptical about those "entangling foreign alliances" that George Washington warned against - and the money involved in paying for such things.
More importantly, in recent years and with hopefully a little more maturity in my thinking, I've become more specifically skeptical of our ability to do everything for everybody. We've only got so much money, so many soldiers, and limited US public patience. Thus, I would identify my own qualms about interventionism as reflecting more my conservative practicality rather than my more idealistic libertarian beliefs.
But there's a school of thought in favor of engagement in the world. The world does perhaps need at least a little bit of policing, someone capable of keeping a lid on the worst bad guys, and keeping trading lanes open. To the extent that this has merit - which seems considerable - America is at this point the only possible candidate for the job.
I don't know that we should consider ourselves morally obligated to take action every time there's a problem anywhere in the world. Plus, again, there are the limits of how much we can do. Plus, of course, who died and made us boss? (Answer: a lot of brave US soldiers)
Still, like Gary Johnson in Team America, I don't want the power or responsibility. But if the US doesn't assert itself, then a lot of bad things happen to the rest of the world, and ultimately to US. Hitler and the Japanese weren't our problem until Pearl Harbor - which left millions dead before we got involved, and a much deadlier mess for US than if we'd all smacked Hitler down years sooner.
It's tough knowing what to do in the world, but this consideration just becomes more difficult when ideology takes over the discussion. Thus, when someone invokes the word "empire" in a discussion of US policy, that's pretty much a sign that you needn't bother talking to them. It's like saying that someone is a "racist." You've attached that stupid label, therefore you have proven your case. Quad erat demonstratum. Empire is bad, m'kay? If we have any troops in any other country in the world, then we are building "empire." Therefore, by definition we are cast as moustache-twirling villains.