There is not a conflict between “it’s OK to be angry” and “it’s not OK to lose control and explode at other people in anger.” 

Anger is a feeling.  It exists inside your mind.  Like other things that exist inside your mind, it can be expressed, and we have a suite of basic general-purpose rules for doing that in an acceptably civilized way.  Use your words.  Be courteous.  Give others their due.  Y’know, basic stuff like that.

I am breathtakingly angry, like, all the time.  And this is not a secret from the people around me!  They are keenly aware of it!  I publicize the fact frequently and with vigor!  And this is not particularly a problem, because I do not do the sort of intemperate things that people do right before they complain about how they’re “not allowed to be angry.” 

Self-control isn’t always easy, and it’s harder for some than for others across the board, and I understand that.  I sympathize with people who fail at it.

That doesn’t mean that it’s not important.