Light didn't have the right to judge anyone. Though it is true that if the Death Note had fallen into someone else's hands, they could/would have used it for worse purposes, like revenge or greed. However Light thought what he was doing was noble, and in his mind it was the right thing to do, and it was a form of divine justice. However it was never his decision to make, he himself wasn't perfect, either. And in the end he became one of those he had been using the Death Note to kill, and also thought of himself as a 'god' because of his ability to do so. A bad person? I don't know, because I don't judge.