Objection 1. It would seem that the incontinent in anger is worse than the incontinent in desire. For the more difficult it is to resist the passion, the less grievous, apparently is incontinence: wherefore the Philosopher says (Ethic. vii, 7): "It is not wonderful, indeed it is pardonable if a person is overcome by strong and overwhelming pleasures or pains." Now, "as Heraclitus says, it is more difficult to resist desire than anger" [Ethic. ii. 3. Therefore incontinence of desire is less grievous than incontinence of anger.
Objection 2. Further, one is altogether excused from sin if the passion be so vehement as to deprive one of the judgment of reason, as in the case of one who becomes demented through passion. Now he that is incontinent in anger retains more of the judgment of reason, than one who is incontinent in desire: since "anger listens to reason somewhat, but desire does not" as the Philosopher states (Ethic. vii, 6). Therefore the incontinent in anger is worse than the incontinent in desire.
Objection 3. Further, the more dangerous a sin the more grievous it is. Now incontinence of anger would seem to be more dangerous, since it leads a man to a greater sin, namely murder, for this is a more grievous sin than adultery, to which incontinence of desire leads. Therefore incontinence of anger is graver than incontinence of desire.
On the contrary, The Philosopher says (Ethic. vii, 6) that "incontinence of anger is less disgraceful than incontinence of desire."
I answer that, The sin of incontinence may be considered in two ways. First, on the part of the passion which occasions the downfall of reason. In this way incontinence of desire is worse than incontinence of anger, because the movement of desire is more inordinate than the movement of anger. There are four reasons for this, and the Philosopher indicates them, Ethic. vii, 6: First, because the movement of anger partakes somewhat of reason, since the angry man tends to avenge the injury done to him, and reason dictates this in a certain degree. Yet he does not tend thereto perfectly, because he does not intend the due mode of vengeance. on the other hand, the movement of desire is altogether in accord with sense and nowise in accord with reason. Secondly, because the movement of anger results more from the bodily temperament owing to the quickness of the movement of the bile which tends to anger. Hence one who by bodily temperament is disposed to anger is more readily angry than one who is disposed to concupiscence is liable to be concupiscent: wherefore also it happens more often that the children of those who are disposed to anger are themselves disposed to anger, than that the children of those who are disposed to concupiscence are also disposed to concupiscence. Now that which results from the natural disposition of the body is deemed more deserving of pardon. Thirdly, because anger seeks to work openly, whereas concupiscence is fain to disguise itself and creeps in by stealth. Fourthly, because he who is subject to concupiscence works with pleasure, whereas the angry man works as though forced by a certain previous displeasure.
Secondly, the sin of incontinence may be considered with regard to the evil into which one falls through forsaking reason; and thus incontinence of anger is, for the most part, more grievous, because it leads to things that are harmful to one's neighbor.
Reply to Objection 1. It is more difficult to resist pleasure perseveringly than anger, because concupiscence is enduring. But for the moment it is more difficult to resist anger, on account of its impetuousness.
Reply to Objection 2. Concupiscence is stated to be without reason, not as though it destroyed altogether the judgment of reason, but because nowise does it follow the judgment of reason: and for this reason it is more disgraceful.
Reply to Objection 3. This argument considers incontinence with regard to its result.
Source: Summa Theologica (New Advent)