I'd go further and say that everything one does is for the purpose of being entertained in one way or another. Bob Dylan said "Why would you pay to do something if you're not going to be entertained? Are you going to pay to go get whipped? And, if you do, aren't you going to be entertained?"
Well the formula is pretty simple. Special effects, good looking women, violence, low-brow humor, voila! When I see a movie like Kick-Ass I'm not thinking "wow I sure hope this screenplay is tightly constructed and the dialog and acting are superb". I am expecting to see a little girl use foul language and a lot of violence and silliness. But perhaps thats just me, I don't go to the theaters unless I've researched what it is I'm watching.
I knew what I was in for and usually I'd enjoy it. I just thought it was badly done. But my finger is obviously not on the pulse. I didn't think The Hangover was funny at all either and most people did. I do like a lot of Hollwood movies though, even formulaic ones, if the writing is a bit stronger or there's some other special something to recommend it. I'm not generally a snob about movies. I like a lot of mainstream movies and I like a lot of other movies too. I just didn't like this one and I was disappointed because I'd thought I would.
I've never really been into comics, so usually when I see these movies I get some crap like Transformers, Spiderman 3 or Iron Man 2... Kick-Ass was at least refreshing to me in that sense, it didn't take itself too seriously. I respect that.