You may learn from your anger, but you cannot learn while angry. Anger is an intellectual ditch: no movement possible, all reality transformed into a dark hole in which the soul gradually buries itself in an attempt to justify its perspective by denying the possibility of light.
The required spiritual change does not necessarily entail denying the condition that occasioned the anger, which might (or might not) be quite real and genuinely destructive, but merely learning to regard the sober understanding of corruption, and the inner detachment from folly — rather than the annihilation of corruption and folly — as the truest victories. The problem, once again, is that you cannot learn this while angry.
Anger arises, and feeds itself, as long as the soul’s primary inclination is to exact justice, rather than to know it.