A little more on last week's point about the limits of the question, "Does doing X make me a bad Catholic?"
CCC 2267, which has been quoted often in the last week and a half, says this:
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, non-lethal 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 are 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 non-existent."* * John Paul II, Evangelium vitae 56.
The standard minimalist approach to this is to point out that the sentence beginning, "Today, in fact," is not Catholic doctrine but the personal judgment of Pope John Paul II some time around 1995. As such, one would not be a bad Catholic if one were to arrive at a different judgment about how frequent are the cases in which the execution of the offender is an absolute necessity.
The problem with this approach is that it completely separates the teaching of a principle and its application. Moral principles like the Church's teaching on the death penalty are not expressed as exact formalisms that can be applied with objective rigor in concrete cases. An application of a moral principle is itself a lesson about that principle.
When the blessed John Paul II wrote that "cases of absolute necessity...are very rare, if not practically non-existent," he wasn't merely giving his personal opinion, he was illustrating what it means that the death penalty must only be used in cases of absolute necessity. The basis of his statement is not a mystery. The "steady improvements in the organization of the penal system" is not an occult matter. We aren't left scratching our heads and wondering what leaps of logic he made to arrive at his judgment.
So while I won't call someone who asserts that cases in which the death penalty is absolutely necessary are not very rare a bad Catholic, I will wonder whether they really understand what "absolutely necessary" means.