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Hitler and Napoleon were angry little men, look what they managed to do before their eventual demise, evidently many others drank their perceived poison whilst they exacted their revenge for all the things they perceived as being the cause of their contextual plight. 

Also if the above were followed to the fullest extent things like apartheid would still exist today and I very much doubt people would have had the freedom to even choose to seek wisdom in Buddha's words.

Are you sure the Buddha said that??! Its like some else just makes this stuff up and pretends it was said by the person.

From the context it was intended it might be very true, but what can you do till the anger is ready to be relinquished, especially if the cause was something that hadn't been caused from a fault of your own having done your best to avoid it to begin with? For some people it might be the case that in being angry for so long they forget why they were angry to begin with to maybe eventually realize they wasted a large part of their lives and mental energy being angry having maybe reached a point or place in life where it doesn't seem to matter anymore in maybe coming to certain realisations.

Obviously on an individual level some things can't be fixed until an unforced realisation or state of mind is reached.

Although Buddha was an advocator of peace and an advocator of protest through peace in his quest to understand the injustices of this world caused by others, I'd be more inclined to think he would more likely say do what you can to bring some notion of peace, but generally what will happen will happen and couldn't be any other way in the more extended general sense of the whole Karma thing.