Mm for instance, I think in some contexts markets are pretty powerful, like prediction markets are pretty good at predicting things. (Not saying they're flawless -- polymarket likely overpredicted Trump's victory). Or that benign-looking regulation is frequently detrimental to the public -- while not libertarians at all, Abundance makes a good case for repealing a lot of regulation related to construction. Such regulation is often motivated by people who want to preserve the value of their homes, even though on the surface it appears to be about environmental concerns. (Obviously, I think the environment is important, so we shouldn't just repeal everything. Just that we should be more critical of such regulation.) Another example is how the U.S. banned civilian supersonic aviation in its airspace because of disruptive sonic booms; apparently the technology now exists to keep such booms very quiet, but the regulation persists, because it's not booms which were banned but instead supersonic speed as a proxy for booms.
Probability of nuclear war rises with number of states having nukes. It's best to keep that number as low as possible, so I would not think it wise for Greenland to have nukes. It would not be a sin for Iran to have them, though, given Iran's allies aren't exactly offering a nuclear umbrella.
When talking with libertarians you should keep in mind they have completely different axiomatic values. It is often the case that they understand a certain policy would be on net bad for everyone, they simply don't care. They are rarely utilitarian about those issues.
I get along much better with libertarians who justify libertarianism with values extrinsic to just "muh freedom" -- they are usually much more willing to yield ground in places where I can convince them that a libertarian policy would be net negative, and they have also moved me to be more open minded about some things I thought I would never agree with.
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