I have quit/turned down jobs for idealistic reasons, although I realize we live in the real world. In the end I didn't prove a point to anyone but myself, but I consider that to be a worthwhile goal.
Any job that requires an element of deceit if off limits to me, so that rules out about anything that includes advertising. This includes fast food joints who show a picture of a great looking cheeseburger on the menu, and then serve you a shriveled up sloppy piece of pathetic meat on a stale bun.
Any job that requires me to forfeit my personal liberties is off limits to me. This, of course, includes jobs with drug testing; even those sneaky employers who tell you before hand that a test is coming so you can pass. To me that is the ultimate hypocritical attitude and I can't associate with someone who thinks it's okay. That's like saying 'I don't care if you do drugs, but I want it to seem as if I care on paper so I can get the government incentives'. This also includes jobs that ban people from discussing their work on the net. Protecting trade secrets is understandable, but that's not what these companies are afraid of. They just want to stifle negative opinions.
I've quit a job once because they tried to promote me. It was one of those 'you get a title and responsibility but no extra pay' types of promotions. I was so offended that they would attempt to delegate responsibility by insincerely flattering me that I walked out. Jobs that manipulate are off limits to me.
The other thing that makes me quit a job when the employer expects flexibility from you, while remaining completely rigid themselves. I had a factory job that docked your pay 15 min if you were 1 min late. Even if you were standing in line to clock in. Yet they wanted you to postpone lunch if an order needed to go out quickly, and stay an extra 10-20 min after a shift if things needed cleaned up. That amounts to setting a standard for me that you are not willing to live up to yourself.
So basically hard and/or dirtiness does not factor in to me, it's all about respect and being forthright. With all these pet peeves one might wonder if I ever found a job I liked. I delivered furniture for a small company for 6 years. They appreciated the time I put in and treated me as if I was a help, instead of a necessary burden.
I can afford to have this attitude because I have absolutely no one depending on me but myself. If I had a family to provide for, or coveted things like jet skis, it would be a different story.