Here in germany the "nothing to hide" argument is mostly used by the spokespeople of the ministry of state security with an implication of crime as defined by the law as written. But let's not focus on the finer points of morality. More important: even if we go from "right to hide some thing evil" to "right to hide some thing" we are not even close to privacy. Because privacy is not about hiding some information about oneself, it is about the right to have some level control about personal information.
A level at which almost everyone suddenly understands privacy is sexuality: no matter if you want to keep your sexuality hidden or not, no matter if you publish on pornhub or not, privacy is the right to not be filmed in your bedroom without your consent. Privacy is not about hiding.
Such a distinction doesn't matter much.
Evil is in the eye of the beholder. E.g. for Southern racists in the 50s, the fact that one supported and funded black rights would seem "evil" as well.
As long as what X (= you or someone you know) said or did appears evil to third parties (government, society at large, their boss, private interests, etc), and leaking this could have negative consequences against X, that's enough to justify the argument made.
Whether the thing is actually evil or good is not really relevant (that implies some fixed moral order for eternity and for everybody within a certain time).