It’s because the good libertarians just call themselves anarchists or maybe even syndicalists.

Your typical online libertarian is like the stereotype of the “parasitic socialist” who doesn’t want to work and just wants free stuff.

To continue my gross simplification: libertarians want to be able to boss around poor people using their wealth, but don’t want poor people to be able to band together to stop them from doing so. And they definitely don’t want to share their wealth.

I used to consider myself a libertarian because I believe, as you say, that government authority is responsible for all these things and we are better off without it. I never went to the extreme of saying we should get rid of it (I can elaborate, but that’d be digressing). But I still believe in the core values of libertarianism.

Thing is - in all the libertarian communities I’ve visited/joined online, I’ve noticed that the other libertarians treat these values not as principles but as aesthetics. Half of the activity there (the other half was criticizing everything the government does, whether it’s good or bad) was about using the NAP as a creative limitation - how do we control the populace without technically infringing on individual freedom?

• Want to censor people, but you can’t because “freedom of speech”? Just take their stage from under their feet (other than the air though which their voice vibrates, everything was considered “public property” which they are not allowed to use for their “personal” agenda) or have their employers fire them (they don’t have to employ them - that would infringe the employer’s liberties)
• Want to enforce regulations? Just use insurance companies. Make it so it’s impossible to operate without insurance, and then the insurance companies can impose whatever regulation they want or else they won’t insure you.
• Want brutal law enforcement, but that’s a literal violation of the NAP? Just call it “private security companies” and everything is okay. Actually, the idea here is that the private security companies won’t want to fight each other, so they’ll come to an agreement between them and force that agreement on their customers. And if that sounds like how organized crime families work, then
• Slavery is a big no no, so how do we get slaves? Debt slavery to the rescue!

And these are the relatively reasonable things. At some point I had to conclude that either none of them was a true Scotsman libertarian - or that maybe I should just abandon libertarianism itself (though not necessary all its teachings)

Modern, specifically American libertarians are imposters. Rejecting basic concepts of actual libertarianism like public ownership of natural resources. And are ideologically at least (economic) liberals. Not libertarians. Who chant weird self defeating tautologies that have nothing to do with libertarianism like the Non Aggression Principle.

Basically they’re Libertarians in the same fashion Marxist Leninist are communist. Not.

legalization of slavery

I’m sorry but do you think private commerce had zero interest in the trade of flesh?

A government is not some magic special construct. Am authoritarian governance system is the same whether it’s enacted by something with a national moniker or a corporate one.