Becoming a walking bomb capable of leveling a city is not something a neutral or good person does, at least I wouldn't think they would. At least Wyll only screwed his own soul, Gale's on a whole other level of "fuck the consequences".
The point is that Gale had no idea those would be the consequences. He knows it now and can be held accountable for what he does with that knowledge, but he didn't know it then.
