There are, generally speaking, two kinds of libertarians when it comes to foreign policy: those who have accepted non-interventionism as a moral doctrine, and those whose criticisms of excessive military involvement abroad are based on utilitarian concerns.
The ones who express non-interventionism as a moral doctrine are usually implicitly accepting the statist concept of national borders as a fundamental part of the moral case for their version of "non-interventionism" which is really just a form of cynical nihilism.
Either it is moral to use force to stop someone from violating the rights of others, or national borders create a situation where defending the defenseless is a moral imperative on one side of an imaginary line and an immoral exercise in authoritarianism on the other side of the imaginary line.
I don't hear "non-interventionists" criticize JFK for using military force to integrate universities in Alabama. I don't hear (many) non-interventionists criticize the philosophical premise that fighting the civil war to end slavery was a moral imperative. You just don't hear these appeals to problematic concepts like sovereignty when people talk about something happening within the borders of the United States. But, the minute a tin pot dictator abroad starts slaughtering dissidents, non-interventionists can't get enough of their sovereignty cool aid. They can't get enough of the "we can't impose our will on them".
There are very real utilitarian problems with a great deal of what the US military does. The fact remains, though, that non-interventionism is an inherently statist doctrine that creates the moral imperative not to defend the innocent if they are on the wrong side of an imaginary line.
I'm sure many people will counter with smug claims about how they think individuals should be able to help but they don't want the state doing that. This is, in most cases, a federal crime, but I never hear them vocally opposing the variety of laws that make it so--if they ever mention it, it is as an afterthought, to try to shut up guys like me. Why? Because, fundamentally, people who espouse the doctrine of non-intervention as a moral of philosophical doctrine care more about their pretty little philosophy being wrapped up in one simple and consistent package, like a Christmas present they can open at any time and put forth a dogmatic "principled" argument that requires no consideration of reality.
Non-interventionism, is quite simply, a filthy ideology that has as its natural conclusion the vile defense of genocidal dictators, or at best, smug indifference towards the suffering of millions.
This is very different than a utilitarian critique of the consequences of a given policy move--something where libertarians add substantial value. When people start with the premise that all people have the same rights and that when even one person is deprived of liberty it is an assault on all people--and then proceed to examine reality and conclude that some type of intervention would likely have bad real world consequences, this is consistent.
But please, by all means, keep promoting the idea that one should sit by as millions of human beings are deprived of an existence proper to humans by tyranny far worse than anything you can imagine at home--it is the surest way to make sure that you get nowhere in politics. And if you really believe that "its none of our business" or "but muh taxes" or "but imperialism", you are right where you belong in politics, with exactly the amount of influence you should have, right now. Keep doing what you're doing.
If you want to build a more peaceful and free world, well, I'm on board with that. My philosophy starts with the premise that every human has an equal right to liberty, and that it doesn't matter where they're born or what dictatorial regimen lays claim to their life. I see the world as complex and I see a lot of places where rights conflict and you have to think deeply about the particulars of a situation if you're really interested in building a freer world. I have no time for or interest in pseudopoliticians who tweet nonsense about national borders giving despots the right to enslave entire populations.