Objection 1. It would seem that cowardice is a greater vice than intemperance. For a vice deserves reproach through being opposed to the good of virtue. Now cowardice is opposed to fortitude, which is a more excellent virtue than temperance, as stated above (2; 141, 8). Therefore cowardice is a greater vice than intemperance.
Objection 2. Further, the greater the difficulty to be surmounted, the less is a man to be reproached for failure, wherefore the Philosopher says (Ethic. vii, 7) that "it is no wonder, in fact it is pardonable, if a man is mastered by strong and overwhelming pleasures or pains." Now seemingly it is more difficult to control pleasures than other passions; hence it is stated in Ethic. ii, 3, that "it is more difficult to contend against pleasure than against anger, which would seem to be stronger than fear." Therefore intemperance, which is overcome by pleasure, is a less grievous sin than cowardice, which is overcome by fear.
Objection 3. Further, it is essential to sin that it be voluntary. Now cowardice is more voluntary than intemperance, since no man desires to be intemperate, whereas some desire to avoid dangers of death, which pertains to cowardice. Therefore cowardice is a more grievous sin than intemperance.
On the contrary, The Philosopher says (Ethic. iii, 12) that "intemperance seems more akin to voluntary action than cowardice." Therefore it is more sinful.
I answer that, one may be compared with another in two ways. First, with regard to the matter or object; secondly, on the part of the man who sins: and in both ways intemperance is a more grievous sin than cowardice.
First, as regards the matter. For cowardice shuns dangers of death, to avoid which the principal motive is the necessity of preserving life. On the other hand, intemperance is about pleasures, the desire of which is not so necessary for the preservation of life, because, as stated above (2, ad 2), intemperance is more about certain annexed pleasures or desires than about natural desires or pleasures. Now the more necessary the motive of sin the less grievous the sin. Wherefore intemperance is a more grievous vice than cowardice, on the part of the object or motive matter.
In like manner again, on the part of the man who sins, and this for three reasons. First, because the more sound-minded a man is, the more grievous his sin, wherefore sins are not imputed to those who are demented. Now grave fear and sorrow, especially in dangers of death, stun the human mind, but not so pleasure which is the motive of intemperance. Secondly, because the more voluntary a sin the graver it is. Now intemperance has more of the voluntary in it than cowardice has, and this for two reasons. The first is because actions done through fear have their origin in the compulsion of an external agent, so that they are not simply voluntary but mixed, as stated in Ethic. iii, 1, whereas actions done for the sake of pleasure are simply voluntary. The second reason is because the actions of an intemperate man are more voluntary individually and less voluntary generically. For no one would wish to be intemperate, yet man is enticed by individual pleasures which make of him an intemperate man. Hence the most effective remedy against intemperance is not to dwell on the consideration of singulars. It is the other way about in matters relating to cowardice: because the particular action that imposes itself on a man is less voluntary, for instance to cast aside his shield, and the like, whereas the general purpose is more voluntary, for instance to save himself by flight. Now that which is more voluntary in the particular circumstances in which the act takes place, is simply more voluntary. Wherefore intemperance, being simply more voluntary than cowardice, is a greater vice. Thirdly, because it is easier to find a remedy for intemperance than for cowardice, since pleasures of food and sex, which are the matter of intemperance, are of everyday occurrence, and it is possible for man without danger by frequent practice in their regard to become temperate; whereas dangers of death are of rare occurrence, and it is more dangerous for man to encounter them frequently in order to cease being a coward.
Reply to Objection 1. The excellence of fortitude in comparison with temperance may be considered from two standpoints. First, with regard to the end, which has the aspect of good: because fortitude is directed to the common good more than temperance is. And from this point of view cowardice has a certain precedence over intemperance, since by cowardice some people forsake the defense of the common good. Secondly, with regard to the difficulty, because it is more difficult to endure dangers of death than to refrain from any pleasures whatever: and from this point of view there is no need for cowardice to take precedence of intemperance. For just as it is a greater strength that does not succumb to a stronger force, so on the other hand to be overcome by a stronger force is proof of a lesser vice, and to succumb to a weaker force, is the proof of a greater vice.
Reply to Objection 2. Love of self-preservation, for the sake of which one shuns perils of death, is much more connatural than any pleasures whatever of food and sex which are directed to the preservation of life. Hence it is more difficult to overcome the fear of dangers of death, than the desire of pleasure in matters of food and sex: although the latter is more difficult to resist than anger, sorrow, and fear, occasioned by certain other evils.
Reply to Objection 3. The voluntary, in cowardice, depends rather on a general than on a particular consideration: wherefore in such cases we have the voluntary not simply but in a restricted sense.
Source: Summa Theologica (New Advent)