If I have a dvd, then I have the right to view that content in a non-public setting, and also to make limited copies for personal use. (IANAL, but I think this is correct)

So then, what if my dvd gets stepped on? Then I can't watch my movie anymore. I could then go onto one of these sites and download the movie, which I already own the rights to watch, and then make a personal use copy with a dvd-r.

It seems to me that this is legal. If, therefore, the content of the site (torrents) can be used legally, how can the site be held responsible for illegal use?

Isn't that like holding a rental place responsible for people copying their movies, a gun store for armed robbery, or a car dealership for illegal drag racing?