i think the 'patience by choice bit' can be applied to yourself but not others . When you are angry for someone else it gets tricky. i mean someone treats you unfairly and you just let it go and try to be patient with them, fair enough. But if someone is hurting another being and you let it go then i have trouble admiring it as patience. (Obviously if one tries to be patient because intervention could make matters worse than that is something else.)
It comes down to the empathy i guess sometimes we feel angry because we are not in the position to help someone we love, only they can help themselves and they dont . I guess that is the worst kind of anger one can feel and i should know.