I never understood the " none of your business " argument

What is or isn't someones business is completely subjective to the person, you might be doing something really sh$$y and causing damage to you or somebody else, would this be none of my business ? If this is true things like the police or military shouldn't have the right to exist because it's " none of their business " . This is why I laugh every time someone brings up this absurd argument that it's none of my business to know something that I believe will affect me in someway.

Keyword: might

mind your own business

People aren't required to tell other people everything or anything about their lives. If you feel it's something that pertains to you, then you are more than welcome to ask, and they are more than welcome to refuse. And if you don't want that because you feel it affects your life significantly in a negative way, then you are more than welcome to cut ties with people you feel are keeping things from you that are important, and find people who will be upfront with you about those tings. Bottom line, people have every right to keep secrets, but you have every right to choose who is in your life.