Of course you have to respect them, they are humans and having a bunch of people taking pics of you even when you're not "working" could be exhausting.
But it's true that some celebs (maybe a minority, but still) like having their pics taken, or they don't care seeing a fan or whatever taking a pic of them with a huge smile...
I don't like comparing normal people who casually met a star next to them to paparazzis, tbh. For the first ones it is usually a coincidence, but paps can stalk them for hours and even break the rules while taking pics of someone inside a private area, as Robbie Williams lived and wrote on Twitter... Everybody, paparazzi or not, should respect limits, of course.