Meng Yao always had his back against the wall. He is pitiful, but also spiteful. Nie Ming Jue may have been too coarse in his words, but he did have a point. JGY doesn't care about others, in the end he cares about himself.
Ah, the infamous "kicked down the stairs of Carp Tower" scene from the book! Jin Guanyao was pretty much gelled after that point. There's no going back...
Meng Yao thought he was entitled to things, and used that to justify his actions, when he did have other choices available to him, but they wouldn't have lead to him becoming sect leader