In Catholic teaching, anger is a passion. It is morally neutral. It is definitely not one of the virtues. Anger can be informed by reason to contribute to the good, or to do evil.
I think what we have here is a misunderstanding of the concepts behind “virtue” and a possible ambiguity between two slightly different meanings of the word.
Virtue can mean a “good quality.” in other words, patience is a virtue in the sense that patience is a sought after trait in human beings.
Virtue, in the classic Aristotelian and Thomistic sense is a “power” or “faculty” that enables particular outcomes. When we use the word in phrases like “in virtue of” or “enabled by” we mean this sense of the word.
Virtues are those faculties or powers that are part of being human that enable humans to fulfill our intended purpose.
A hammer has “virtues” which are the “great-making” qualities that allow it best to fulfill its function as a hammer.
The qualities of a human soul that “empower” it to be the best possible example of a human soul are its 'virtues." Since humans, unlike hammers, are active agents, the “great-making” qualities of humans are the faculties that empower or move the human agent to action.
Love moves. That is why it is a “virtue” in this wider sense of being a capacity that enables humans to act. However, when love is disordered and not aimed at proper ends, then the “virtue” that ought to be a “great-making” trait in a human agent is actually the very means by which the agent is disordered and, thereby, lacks greatness.
If the “virtue” or power did not exist in the first place there would be no question of disorder because passive things do not act. Humans are active agents, that is why our “virtues” are the qualities that promote our activity.
In this sense, the existence of any virtue (empowering characteristic) is the very means by which vice is brought about, because vices are also “powered” or “active.” Any power (virtue) is virtuous when it functions as it should, but “vicious” when it does not.
That is why the cardinal virtues each have a deadly sin or vice that corresponds to them.
Anger, of itself, as you have pointed out is neither virtuous nor vicious. It is, however, a “virtue” in the sense of an aspect of the soul (passion) that empowers it towards some end. In the case of anger, as Aquinas points out, that end is justice.
Likewise, we could say, the hero acted by virtue of his love or courage (both virtues) to save the drowning child. Love moves to action. That is why it is a “virtue” in the Aristotelian sense of “power of the soul.” But disordered love and disordered courage (brashness=unrestrained, timidity=overly restrained) are both vices.
We could also claim a hero acts by virtue of his anger to stop a rapist from committing his deed. He intervened out of anger witnessing an injustice about to be committed. Anger, like love, moves to action. Likewise, it is a virtue or “power” of the soul.
Both love and anger require proper ordering. That is accomplished by the faculty of reason properly ordering both powers (among others) toward the ‘good.’ Both “powers” also require a kind of “opposing” or controlling mechanism.
In the case of anger, Aquinas, calls it meekness - the virtue of abating anger. However, if anger is only abated then it cannot move the agent to action when injustice is witnessed. That would be a vice
It could be argued that meekness which is not properly balanced by the virtue of “anger” will acquiesce to evil and injustice will reign because the agent does not properly activate the proper capacity or power - the virtue to be angry at injustice.
It appears that Jesus’ admonition to “turn the other cheek” or the Beatitude lauding “blessed are the meek” is advocating that meekness necessarily excludes anger.
This is a misreading, however, because the options are not “fight (anger) or flight (meekness)” but something in between: anger properly controlled by meekness properly activated, but also anger properly activated by meekness properly restrained. This would be a virtuous state of the soul - one properly ordered towards justice.
Turn the other cheek is not an admonition Jesus would make when witnessing a child being abused. He would NOT advocate standing back and telling the child to turn the other cheek because that is what a good Christian would do. No, we should rightly become angry and be moved to intervene by that anger. That anger would be virtuous BECAUSE it is a power to act for the cause of justice.
