The problem is, there's not really a good way to debate "If you have nothing to hide, there shouldn't be a problem." The person pushing for surveillance is going to argue in bad faith that they're the good guys, and why are you stopping them from catching the bad guys? And there's no counter argument to that because it's very hard to find specific examples of where authoritarian governments overreach and go hard on innocent civilians. I reckon when that happens, they manage it keep it very quiet, since they are authoritarian.
On top of all of that, who wants to defend child pornographers? I can see why a person wouldn't even try to engage in that back and forth. There's just no way you come out on top, because basically your side of the argument would have to come down to "Everyone has something to hide, and we should recognize and protect that." It just doesn't _sound_ good.