Yea that's not inherently a libertarian stance.
Honestly, the inconvenient truth for most of this sub is that it is. Libertarianism is not a self-consistent ideology outside of such egoism.
This doesn't mean Libertarians are "dumb" or that their beliefs are invalid. It just means that their beliefs are either egoist like OP gets at, or more commonly, beliefs of another ideology (usually (neo)liberalism).
For a concrete example, consider a belief pretty much every single Libertarian holds: "You may not shoot someone, be that intentionally or by firing your gun negligently in such a way that another can be hurt."; No shooting people, or randomly shooting your gun into the air or in the city. Basic stuff.
Well, you can apply that principle to non-gun things; You can't stab people with swords, or throw a sword into a crowd. People would get hurt, you're not allowed to hurt them.
And a self-consistent ideology builds all their beliefs as extensions of their base principles. And most Libertarians will agree with the notion that the "don't kill/hurt people" rule applies to all weaponry.
... so what about edge cases? What about anthrax?
Am I allowed to blow anthrax into people's faces? Casually dump contaminated materials into the water supply?
Most Libertarians will agree that no, of course not. People will die, and you're not allowed to kill people. So the government should be allowed to put a "no dumping anthrax you idiot" law into place, right?
You can likely see where I'm going with this. As I've just demonstrated, the "no killing people" principle easily extends out into environmental protection laws. Some Libertarians will start to get uppity, but most still agree that "you shooting your gun in the sky with people around" should be banned, and that companies aren't allowed to dump nuclear waste where-ever.
Though this does beg the question, where does this extending-out end?
And a pretty reasonable answer for that is "so long a reasonable person can foresee that this will kill/hurt people". The ideologies deriving from Liberalism generally take such a stance.
You can't leave your car with no brakes on the side of a hill with an orphanage at the bottom; That's just negligence. You'll find a fair amount of Libertarians still agreeing on this and similar traffic laws. "Don't act dangerous on the road, because you'll kill people, and that's not allowed".
Yet, we do know of plenty of things that harm others, yet Libertarians quite vocally oppose being banned.
Consider the anthrax example, odds are you agree that blowing anthrax onto people's faces isn't allowed and that the government should ban it. Be it under the NAP, or just a general sense of don't kill people you idiot.
So then, what about covid-19?
We have established, through science, that yes, not wearing a mask will lead to increased spread. And that people will die as a result.
Many a (Neo)Liberal will be quick to agree that "Yeah, not wearing a mask will lead to people dying, therefore it's negligent, therefore the government should pass mask mandates."
Yet this subreddit has quite a lot of people who are very opposed to such mandates.
And as OP indirectly gets at, is that not arbitrary? You can't ban negligent actions that get people killed whenever you already don't want to do those actions, yet allow them whenever it's something you do want to do.
To be consistent one has to either accept that the principle of "don't kill people" extends out to mask mandates, or one has to give up the original principle and accept that letting people die through such negligence is fine. "Don't want to catch covid die from stray bullets? Just stay inside!"
Both options are perfectly cromulent beliefs, yet neither are what many would consider "Libertarian".
TL;DR: Most of you are just a bunch of neoliberals who don't yet realise it