As is true for many forms of public service, one's rights get curtailed!

A person's right to free movement, get taken away when one joins the military.  They can be ordered to other lands at any time, under penalty of jail.

A person in uniform can't speak freely either.  They can't speak against the government while in uniform.

A politician entrusted with secrets can't engage in personal behavior if that behavior could lead to blackmail.

Blackmail works quite simply because there is no separation between what his public and what is private.

The whole Bill Clinton defense ("what he does in private is his own business") was a huge lie, an error of the logic of blackmail.

Today, digital blackmail is quite easy to do.  Just intercept the GPS coordinates of two "target" phones over a course of a month, and one can almost prove infidelity. A simple time and space problem.