Lampstand has published a book about this, Capital Punishment & Catholic Social Teaching: A Tradition of Support, and recently, while reading another book, Choosing Life: A Dialogue on Evangelium Vitae, I came across a seminal point rarely noted in the public discussion—for obvious reasons—in a chapter contributed by George Weigel.
“As Father Langan’s essay notes, the traditional response of Western societies to the monstrous evil of willful murder has been capital punishment. For a variety of reasons, many of those societies have now abandoned this practice. Abolition, according to Evangelium Vitae, is the morally preferred course if it can be accomplished in ways that do not amount to an abrogation of society’s right of self-defense. But abolitionists have not completed the necessary public moral argument when they make a strong case, on prudential grounds, for eschewing the death penalty. For if a public moral recognition of the reality of monstrous evil is a necessity in a free society, then abolitionists have to tell us how society is to give expression to its unambiguous condemnation of monstrous evil if it lays aside the death penalty.
“This is not to suggest that the current practice of capital punishment in the United States is essentially a matter of bearing witness to the reality of monstrous evil. Insofar as one can tell, it is a sense of retributive justice, combined with fears for public safety, that motivates most supporters of the death penalty today. Moreover, supporters of the traditional position (Father Langan’s “approach A”) ought to be deeply concerned that the trivialization of the death penalty through ubiquity or frivolous sentencing (which might happen were “approach B” to prevail in either its pragmatic or its symbolic forms) could have the deleterious coarsening effects on the public moral order.
“Still, the free society must attend seriously to its definition of the boundaries of the morally acceptable. And it must be able to give public expression to its absolute condemnation of certain monstrously evil acts. If that is not to be done through the instrument of capital punishment, then other instruments will have to be devised.” (p. 229)
Weigel, G. (1997). Evangelium Vitae on capital punishment: A response to John Langan. In Wildes, K. Wm. & Mitchell, A. C. (Eds.). Choosing life: A dialogue on Evangelium Vitae. (pp.223-230). Washington, D.C.: Georgetown University Press.