Also known as Rubbernecking
You don't want to look, you know it's horrible and probably wrong, but you just can't help it.
I have never seen a train wreck, but I can imagine the feeling. I have seen a car accident, and just had to slow down and look, even though I hate everyone else who causes traffic jams by doing so.
There is something in human nature which loves to do this, which is why Jerry Springer is so successful. People just can't NOT watch the trailer trash even though they hate themselves and feel like a sick voyeur afterwards.