Opinions vary, he's entitled to his.
I enjoy various kinds of movies. I think one of the problems with arguements about this kind of thing is that the people argueing the positions seem to think that people only like one kind of thing, or that liking something that they don't like, means you won't agree with them on something else.
For example, let's look at horror movies, or even specific popular but much maligned generes like "Torture Porn" which hasn't gone as far as it can yet (the definitive movie of the genere has yet to be created). I can enjoy this kind of thing, but I like other kinds of movies as well.
I look at MovieBob's review of "The Expendables" as an example. He seems to totally miss the point that he insulted the viewers who liked it, rather than just saying he didn't like it. Saying "your the worst kind of person" to pretty much everyone.
James Cameron is basically saying that because movies can be better, and enjoyable on some deep level (which is ironic given his creation of Avatar) that this means people shouldn't enjoy putting their brain into neutral and partaking in some intellectual slumming.
"Pirahna 3D" is basically an exercise in intellectual slumming, the purpose is to enjoy the sight of hot bodies, over the top violence, and snicker over the idea of prehistoric fish somehow escaping and making snackfood out of thinly veiled analogies to both the people from "Girls Gone Wild" and "MTV Beach Party" productions.
It's sort of like when I sit down and watch "Torture Porn" as some people call it, I'm a jaded guy sitting down who wants to see something really messed up.... like people who watch horror in general (analyze it as you will). I'm not there for some deep experience.
What's more I'll be honest in saying that most "high brow" horror movies today strike me as being ridiculous. Oh sure, you see some good character development in many cases, but as far as the whole purpose of the movie... the horror stuff, most of them seem to degenerate into wierd stuff happening around a general theme. Half the time "they" (movie makers trying to be high brow) don't even bother to try and justify it, instead spouting "well, the not understanding is what makes it so scary". In a few cases that works, but in most cases it generates the worst kind of junk movie.
To put this into perspective "Saw" is not high art, but it's pretty straightforward. Insane engineer (or his successor) puts people in puzzle traps that require them to mutilate themselves horribly in order to live, which most people are unable to bring themselves to seriously try until the last few seconds of their lives when it's too late. I can understand why waking up in a situation like that is freaky, I understand the motives (such as they are), and how the guy is supposed to be operating.
Compare this to some "horror movies" where say you might watch for like an hour where little wierd things happen (oh gee, that coffee cup wasn't where I left it) followed by some off camera screaming from people, since a lot of times they won't even show a proper ending, finale, or monster. I love coming up with my own ridiculous explanations for some of those movies. For every one like "Paranormal Activity" that manages to be halfway decent (despite the camcorder gimick, which has yet to see the definitive "documentary horror movie" despite the potential, it being mostly an excuse to not show anything), there are probably half a dozen or more where for all we know the actual villain of the whole thing WAS the coffee cup which was haunted... all the guys in these movies perhaps buying from the same cursed coffee cup stall at the same flea market as part of some super "Avengers" type crossover being planned to be released the day before 12/20/12... where all he coffee cups will merge into a giant robot and rampage "cloverfield" style through earth killing everyone and fulfilling the prophecy coming "tomorrow".