I agree with the 'personal experience' reason.
When the organisation hurts you deeply and personally.. when you feel let down by it, when you experience it's indifference towards you, ignored, marginalised, betrayed, lied too, deceived, when your own sense and intelligence are insulted again and again. That's when you have no choice but to step away. To remain would make you party to your own demise and destruction and madness.