Righteous indignation is a good word for it.

I, personally, see it as one of the emotional capacities of a healthy person. Kind of like lust. It can be misused, it can be a big time-waster if you let it occupy your whole life, but it's basically a sign that you have enough energy. If it goes away altogether, something may be wrong.

I had a period a few years ago of something like anhedonia. The thing is, I also couldn't experience righteous indignation, or nervous worry, or ordinary irritability. It was incredibly satisfying to get them back. I'm not a psychologist at all, but I think of joy, anger, and worry (and lust) as emotions that require energy. The miserably lethargic can't manage them.

So that's my interpretation and very modest defense of righteous indignation. It's not a very practical emotion, but it is a way of engaging personally with the world. It motivates you in the minimal way of making you awake, alert, and focused on something. The absence of such engagement is pretty horrible.