The dangerous thing is that there are some busybodies who will believe they are harmed by such things, and so you have to take the argument a step further and precisely define harm to confirm that they have no case. It would be easier if people had a common definition of "if it doesn't involve you then it's not your business".

And the difficult thing about that is that externalities do exist for some things. Pollution affects everyone, for instance, and those externalities need to be accounted for. It's not a trivial definitional problem to distinguish valid externalities from spurious/invalid claims, unfortunately.

Both points are true. I chose these examples in response because they are relatively simple, clear cut examples of "not your business", yet people still try to dictate other people's lives around them.

These people are on one end of the authoritarian spectrum. The other are anarchists, usually ancaps in places I frequent, and they are just as wrong because they are ignoring how people in the real world will actually behave. Negative externalities are precisely the thing that they ignore, minimize, or try to redirect your attention by linking you to a 2 hour video which is supposed to address it but doesn't.

Well, at least they do generally get out of other people's lives though. But it's a system which doesn't work and when it fails, leads to the rise of authoritarians. I wish people were able to understand that policy is a multi-dimensional spectrum and extremes on any one axis are unlikely to lead to stability.