Look, I'm no guru or expert by any stretch, but I do think there needs to be a balance.
To focus all my energy on being angry/resentful/what-have-you without action is pointless.
Also, for me to focus on not feeling angry/resentful/what-have-you means I'm either not paying attention or I don't have a pulse.
I think that the figures mentioned above found positve ways to focus their anger/resenfulness/what-have-you in order to affect change.