Television, as a general rule, is easy to watch. That's part of why people condescend to it: it doesn't take much brain power to enjoy. So when shows produce content that is hard to watch, it becomes both ground-breaking and, well, hard to watch.
Thanks to my Los Angeles based TV consultant, I have recently (and finally) begun watching Dexter. Now this is a show that should be hard to watch - every episode involves several brutal murders, usually quite graphic. Yet you rarely need to turn away. Perhaps we can chalk it up to the dark humor infused into each episode. But I think the reason it's palatable is that the protagonist is a self-proclaimed sociopath with no feelings. While we might pity him because of his lack of emotion, it's impossible to be completely empathetic. As Dexter says in the third episode, "If I had a heart, it might be breaking right now." Well, if he had a heart, ours might be breaking, too. So instead, the real hard-to-watch is a show like Breaking Bad, where the protagonist is a dying man often committing brutal acts of violence to protect his family. Viewers (hopefully) haven't been in that situation, but we have felt pain and we can only imagine the amplified version of that pain that Walter White is experiencing. It's desperate, and it's hard to watch.
Hard to watch doesn't necessarily mean heartbreaking. Recently, it has become clear that the American public has a hard time watching anyone other than typically beautiful people engage in any sort of sexual encounter (exposed recently through a controversial article surrounding Mike and Molly). I wonder if this week's Glee kiss between Mr. Schu (who is meant to be hot stuff) and Bieste (a female actress made up to seem extremely masculine) will re-start that conversation.
One final kind of hard-to-watch is the hilarious kind: the scene when you are so embarrassed for the people involved that you would be crying if you weren't laughing so hard. The best example of this is the Scott's Tots episode of The Office. Watching Michael explain to a group of high school students that he can't pay their way through college as he'd promised so many years ago is The Office at it's hard-to-watch best. You almost want to mute the scene so you don't have to listen to Michael find the right (read: wrong) words to get through the moment. This is the kind of hard-to-watch that makes certain people say that The Office makes them uncomfortable. Well, that's the point.