Privacy is not about secrets.

Privacy is the right to sovereignty over one's personal/intimate sphere - whether it's insight to information about oneself or physical contact. The right to consent, for instance, would be a component of the right to privacy.

It's about power. And by extension it's about the power balance between the people and any intruder of their private sphere, whether it's a friend, a stranger, the public, the state, the law and so on.

In other words, the less privacy there is the less effective power both the individual as well as the entire people have.

That's why it's a basic human right.