No one said he was without fault. After Kagha he calls in someone else to take over, which could end up bad for the grove but we'll have to wait and see how that turns out. Also, I vaguely remember the shadow curse thing having something to do with a family member? Like there was a hint in one of the books scattered around the grove but was later removed, so that storyline is probably being changed. Anyway, his motives could be deeply personal to him and perhaps make him act rashly and without proper consideration. People make stupid decisions because emotions all the time.