Thing is, even in a world where freedom of expression were inviolable (and it isn't quite this world, so in reality, privacy helps support freedom of expression), we'd still want privacy to be a human right. Animals don't behave the same when they know they are always being watched. Pervasive surveillance inhibits thought, breeds abuse and unnecessarily limits human behavior.
Also, in the end, we have the right to have things to hide. We have the right to say and do things we are ashamed of, or aren't sure are right, or we are not ready to defend under scrutiny of society at large. We have the right to share thoughts with others that we are not ready to defend from strangers, even if the law prevents such strangers from hurting us because our thoughts. Society needs to be able to discuss heresy, and revolution, and treason, because what for one generation is treason and heresy, for the next might be justice and freedom. But it also needs to be able to have some of those discussions in dark, private places, because a lot of great thoughts will only ever bloom in the dark. Even if mass surveillance worked (it doesn't), even if abuse could be curtailed (it can't), even if it gave us a world without crime (it won't), the price to pay would be a world where our thoughts are constrained by the fear of other's seeing them in their underdeveloped raw form.
Using "privacy" tends to imply some amount of shame, as if the you didn't (or shouldn't) have the freedom to do that act in the first place. The reason why people see that they have "nothing to hid", is that they have already self-censored themselves away from doing any supposedly-shameful activity.
I've always liked a line from KMFDM's song "terror"[2]
Until people learn this lesson, shame will continue to be used as a threat, and people will continue to see the "logic" in the "nothing to hide" argument.[1] http://www.kmfdm.net/lyrics/terror.htm ( https://www.youtube.com/watch?v=mVhu3pn1Ou0 )