Thinking how anger seems to be a "pure" emotion - meaning it seems to act as a foundation to other emotions. I guess that isn't always true about anger, but I'm entertaining the hypothesis here.
The exception that comes to mind is anger that arises from wanting to avoid feeling another emotion that doesn't necessarily have to be fear, say grief, powerlessness, envy, etc. So in this case the anger would be triggered by something or someone, but the person does not say to themselves, "feeling angry is better than feeling this other emotion underneath the anger." I would guess it may be a better description to say, "I'm angry because of this trigger leads me to interpret my situation as needing anger as the necessary response."
Having witnessed that chain of thinking in myself, it led a conviction that there are always more possible responses available - and usually there are responses that are much more constructive than anger. But sometimes, anger is the best choice and not purely an "out of control" response.
I have also witnessed how a close friend formed a reactive chain of emotions, with anger on the tip of the iceberg. It took him some time to observe his anger; it happened in sequence with the closer feelings behind it, driving the anger. Certainly anger feels more powerful than to feel these "weaker" emotions, (such as sadness or vulnerability.) A person would probably have to feel safe to uncover these other emotions. So I'd agree that there can be some sort of fear mixed into anger, but not always.
Also, I can think of circumstances where anger is meant constructively. Anger can be displayed as a control issue or other form of a demand for respect or to have priority. It's constructive because the anger is used to draw boundaries for a trespasser.
What about the sort of anger that acts as a display to have a certain calculated effect on another person for an intended, justified reason? I'm thinking of the tactical displays that someone I knew has used quite liberally with the justification that he is doing it order to "transform" someone else or teach them. Isn't another example the anger that a parent displays with the calculated purpose to give a child some of the wrath of the world upon them, but not the full effect ?
Also, think of straight old manipulation, the motive of which can be of questionable or unknown priorities. Whether the manipulation is constructive or not is certainly a value judgment. The fury or intensity of anger makes the angry person feel powerful & unpredictable and has the effect of intimidating others; for instance the manipulative warning/threat of "you don't want to be my focus while I'm crazed by anger that I can't control."
I think anger is a positive emotional response when there are certain boundary issues that a person is convinced should be rigourously enforced. For instance, when a recalcitrant is trying to "get your goat" purposefully just to see how irritating they can be or what they can get out of you. From their point of view, they're merely investigating to find out you will react in a conciliatory way of benefit to them.
I'm thinking of other sorts of anger that can act like vigorous resolve. What about the anger directed at oneself for the purpose of goading yourself into action or admonishing oneself to be more mindful? For instance, the anger of someone who is quitting smoking; every time they want tobacco, they say "NO" with the emphasis of the anger directed to buck the addiction. I'd say in that case that anger is a positive response to the coersion of a situational nuisance.
What about regarding the emotion of anger as being purely a way of generating lots of energy and pointing it somewhere on purpose? Wouldn't that attitude take away the value judgment that anger is "good" or "bad"?
Really, any emotional feeling could be substituted for anger here. See how much information you can learn about yourself. Take away the value judgment about whether the emotion is good or bad.