Why should the law care about what I do behind closed doors?

It shouldn't to a point.

Society sets laws announcing those actions that it deems unacceptable in polite society. If evidence appears that causes a reasonable person to suspect that illegal activity is going on, society should investigate. Of course society might find itself having to jump through hoops by adhering to constitutional law. It cannot just invade your personal space and demand to know what you're up to just because they don't like you.

Your speech is free. But if it causes malicious harm to someone, you can be sued.

I have been married for 34 years, and I found out my wife lied, and cheated a lot back before we got married. Does she not change, or is it possible she is still a cheater?

If evidence arises that you are doing these things behind closed doors, don't you think the government has a moral obligation to investigate?

The law shouldn't care (if you are a law abiding citizen) about who you take into the bedroom as long as they are consenting adults. How many guns you own. What you eat for supper. What kind of TV shows you watch. Whether you watch porn or not.

Liberty is not boundless. It does have its limits.

What is the opposite personality type of someone with ASPD (antisocial personality disorder)?

The law doesn't care about what you do behind closed doors as long as it is within the bounds of what the law allows.

But what if you're raping little girls behind closed doors? Killing gay men? Watching child porn?

You can stand on a public sidewalk and take pictures of my house. You can't walk into my house uninvited and start taking pictures.

How did Farrah Fawcett die?