Which again, is because its an explicit violation of social norms. One person doing anything different is always creepy because it's asking all sorts of questions: why are they doing it? why would they be doing it? how dangerous do I think this person is?
If you're filmed by a 1000 cameras a day, you're not going to care because it's the norm. In fact, if they were just a facet of daily life (people have Glass for example) then no one is going to care. And yet, one guy coming up out of the blue, with no social reason to be there, just staring at you, will always be creepy.