Not only is it not sinful for us to be angry, there would have to be something wrong with us if we reacted any other way when confronted with certain situations. I have been accused of being an angry young man at times. Guilty as charged. These are only a few of the things that make me angry. Space is limited, but you get the idea.
Anger is a very real emotion and can be a great motivator if channeled properly.
Be ye angry and sin not. Let anger cause you to do something about things that are wrong. Anger caused Saul and Jeremiah to do some things they wouldn't have done otherwise. Some things ought to make you mad enough to do something. Go for it.