Managing anger, our own and other people's, is a difficult thing.
Anger is scary - "I am acting without any concern whatsoever for the consequences" is disturbing, as it inherently breaks our theory of mind. You usually cannot predict the actions of someone that is genuinely angry as those of a rational agent, and when the prediction engine that is the human brain breaks down like that, it gets upset.
Anger can also be genuinely dangerous when coupled with the power to do harm (whether physical, social, financial, professional etc) to another.