(from FabioAEsteves). "Don't confuse privacy with secrecy. I know what you do in the bathroom, but you still close the door."
* I might be picking a big booger with my pointer finger.
* I might be cleaning my butt in ways which are offensive in your culture, whether using my right hand in the India, without TP in the US, or in a hundred other ways.
* I might be managing a really nasty fungal growth somewhere you can't see.
* I might be pleasing myself.
* I might not be washing my hands after I pee.
* I might be inspecting a polyp for cancer.
* I might be writing "For a good time, call" graffiti, leaving the phone number of your mother/sister/daughter/wife.
* I might be dealing with my period.
... and so on.
But jokes aside, the quote is direct anti-symbolism to the "But I have nothing to hide" and found it pretty effective, even in its silly nature, when arguing with people who are too eager to give up all privacy.
1. You did something wrong.
2. Someone else wants to do something wrong to you.
The first is in your control. I think I've acted with sufficient integrity for my life that I have nothing to hide which might land me in trouble.
The second is out of your control. There are unreasonable people in this world. If you have a stalker, you don't want them to know where you are. If your spouse cheats on you and leaves you, you might have a custody battle on the line. If your government goes the way of Germany or Russia circa 1940, you might want to hide your ethnicity or political beliefs. A police officer is investigating a crime, when someone you didn't like was killed; you didn't do it, but time, place, and motive are all there. None of these are particularly likely, but they do come up.
I have one person in my life, and to protect myself from them, I have a limited online presence. I use fake names, and my LinkedIn stopped updating a few years back which limits career prospects, but it's a sacrifice worth making. I let out a lot of information before that, which was a mistake. I went through some legal disagreements at one point, where another party acted unethically and decided to extort me. These things aren't in your control.
When I was young, I had nothing to hide. When I was older, I learned information is power, and information asymmetry can help you or hurt you. With that wisdom, I now have a lot to hide, and I advise younger folks to be mindful of their privacy.
I intentionally listed a lot of different things in my post, with fault lying in different places or nowhere at all, to give an idea of the variety of reasons one might want to hide something.
Why do we like to defecate in privacy? What is the evolutionary reason? Animals do this too. Dogs only get to business when you give them some privacy and they like to get in the bushes if they can. I would assume it's an instinctive drive to get away from the community, to go somewhere with little social activity, so we don't make our living spaces dirty and infectious with our feces.
I don't think this is the same kind of thing as trying to keep one's political opinions or salary private.
You probably misspelt "Animals", but "niemals" is German for "never" or "no way". Gave me a chuckle in context.
On topic: there's probably more to it in humans, because animals don't have cultural phenomena like shame about their sexual organs, making embarrassing noises or smelling bad.
I would say the parallel with defecating in private is valid, as it can lead to the same perceived loss of social status as "not earning enough" or "having an unacceptable opinion".
Not only that, but the community isn't better served by someone shitting in public. You can make the argument that if everyone's salary was public information the community as a whole would be better off. Yet we still have people at all points on the income spectrum hiding their salary for various reasons.