Because Giving birth to demons and burning people alive is a good thing.
I did not say she was "good", noone is in the entire series, they all follow their own (selfish) interests, using methods like assassination, betrayal and double crossing at every step, not fulfilling agreements and so on.
An honorable man is a dead man, as was clearly shown in the first season. It is a world of vipers, self interest and power.
After all, "when you play a game of thrones, you win or you die", and nobody wants to die.
I said that I like what she is trying to accomplish, which right now I am not sure if they have mentioned it already in the series, have not watched the finale yet.
It is not only the knowledge of men (which is a big tool as it is a game of men and women), she also has the fire visions and other tools from the Red God, which might help her. And of course, like any other character, she will probably have big trouble with a few things.