Don't be ridiculous. The Forsaken are empty, dead shells of what they used to be. They came into existence from suffering and hate, and it is all they have been dealing with ever since. Wherever they go, they try to destroy life, corrupt it, and make a mockery of it.
Sylvanas had her revenge on Arthas, the only good thing to do would be to leave the land alone and let the day stay dead. But no, they have to linger on and make everybody else's existence a misery. Since Sylvanas is originally a good person, I can only assume that the state of undeath twists the mind of her and her minions. In that sense, they have lost their individuality and freedom - and it would be a merciful thing to put them out.