When people think of anger we normally think of the raw, hot-heated type of anger, but there are actually many types of anger. While I mostly agree that the raw anger that you are describing is not a good thing, I do think it can track things in which we are not rationally thinking. For example, I might be mad about my girlfriend for not cleaning her dish after she eats and I overreact and scream at her. I've told her numerous times and she doesn't get it. Really, I'm not mad about the dish itself, but the fact that my girlfriend is not taking my feeling seriously (or something like that). Secondly, some anger, I believe, is extremely important. Not the anger you are describing, but what is commonly called "moral anger". When one views someone being discriminated against, or when they see someone has been wronged, one can get angry. This is not the hot-heated anger, but the more rational moral anger that one feels when certain things, such as an injustice, has occurred. I would argue that this anger is needed for, among other things, motivation to act against such injustices.