It has always been my philosophy that what is "good"can not defeat what is "bad". There are many good examples I could use to explain this but I'm going to go with the Death Penalty:
A person commits a heinous crime, and is sentenced to death. The jury, the prosecutor, the judge, the state, etc., are killing a person because that person commited a heinous crime. How is that good defeating bad? You have a group of people commiting a similar act--whether justifiable is irrelevant, whether deserving is also irrelevant--yet a similar act, that by their law makes it good, or "okay".
We know, by historical accounts, and by present accounts, that it is not a detterent yet an excuse given by many. Also, an excuse given is "an eye for an eye", yet it seems when that phrase is used it only adheres to the act of murder, and no other crime. At least in the "civilized" parts of the world.
Committing the same bad thing that one is punishing the other for, doesn't make those who are committing such acts as being "good", nor does it mean they are still good afterward.
I guess all those religions out there that state: all you have to do is repent, and you will be forgiven, and be a good person is there solely to comfort those who believe they are good when in effect they are far from it.
Good is pure in its form and meaning, and can't be imperfected. Therefore the word, itself, really has no meaning. No one is good, especially if they seek forgiveness, or justification for everything they do.
Only thing, in my opinion, that can defeat bad, is those that which are, or who are, bad themselves.
A somewhat similar example is that character in Serenity (the black guy, can't spell his name off the top of my head, and I am doing this over the phone) where he wasn't of the illusion that a person like himself would live in such a "good world", though, by the end of Serenity, we saw those who slated themselves as being good actually were not.
My apologies if I am coming off a bit incoherent, as stated: I am doing this over the phone, and it is a bit much in way of posting by this manner.