1.) No ******* ****. When's the last time anyone felt sorry for someone getting what they deserve? That's kind of the whole point behind punishing someone.
2.) Because whether you like it or not, life ain't always fair.
So whenever you are mistreated, you just roll over and say "hit me?" If a prof marks an answer wrong, and you believe it's right, you don't fight it? If your roommate welches on the rent and you have to pay it, you don't try to get your money back from him/her?
If something is wrong, speak out. Stand up for yourself. Stand up for others.
Nothing will change if people don't speak out.