Question:
Answer:
One might argue that the application of capital punishment in a particular instance was unjust or excessive, or is, in general, an excessive penalty. But it would be wrong to assert that the death penalty is always and everywhere a mortal sin, as if it were an intrinsic moral evil like abortion and euthanasia.
The Church has always taught that the death penalty can be licitly applied as the just punishment to some serious crimes even if in more recent decades the Church has generally discouraged this form of penalty, also known as capital punishment.
If a Catholic were to hold that the Church has erred by definitively teaching moral evil on a grave matter for centuries, that would be an even more serious and erroneous charge and would also call into question Scripture. However, not knowing a person’s subjective disposition, I wouldn’t hazard to evaluate his subjective culpability—recall that there are three components to a mortal sin (see the Catechism 1854-64)—and I would encourage you to refrain from doing so as well. Rather, simply and calmly explain the Church’s teaching and point the person to the Church’s official teaching on the matter:
Assuming that the guilty party’s identity and responsibility have been fully determined, the traditional teaching of the Church does not exclude recourse to the death penalty, if this is the only possible way of effectively defending human lives against the unjust aggressor.
If, however, nonlethal means are sufficient to defend and protect people’s safety from the aggressor, authority will limit itself to such means, as these are more in keeping with the concrete conditions of the common good and more in conformity to the dignity of the human person.
Today, in fact, as a consequence of the possibilities which the state has for effectively preventing crime, by rendering one who has committed an offense incapable of doing harm—without definitely taking away from him the possibility of redeeming himself—the cases in which the execution of the offender is an absolute necessity “are very rare, if not practically nonexistent” (CCC 2267).
Pray for the person involved and continue your friendship with him, planting the seeds of goodwill along the way. In time, he hopefully will see his error. For further reading, please see this article by Tim Staples.