I would say many people are put off by the morality of it. Sure you're helping people in oppressive regimes avoid censorship, but you're also helping scum in a way many people aren't comfortable with or want to be connected with.
TOR interests me but I'd never run an exit node because I'm assuming one of three things is gonna come out of it: dissidents, criminal activity, or spook traffic (it was literally made by and for naval intelligence /the CIA).
You can make an ethical argument for the first one but I still don't want any of those three running out of my machines...