So the pope may be fallible on the issue?
Well, the extrremely conservative Catholic, Antonin Scalia, sure seems to think so.
The pope is only deemed infallible when he chooses to speak from the seat (ex cathedra) of the papacy on matters of faith and morals. While the death penalty is certainly a matter of morality, no pope has chosen to assert an infallible opinion on the subject. (Infallibility is only 134 years old and it has only been invoked twice. No one (well, except maybe Cardinal Ratzinger) believes that the pope is infallible every time he issues an encyclical or other proclamation.)
from Vatican Council II
How is that conservative Catholics chide liberal ones over and over for not giving loyal submission, then when it’s their pet issue, it’s suddenly “oh, that’s never been addressed ex cathedra.”
Take that up with Tony Scalia.
I happen to agree with the pope on this topic.
A more nuanced response would get into whether giving “in a special way” “loyal submission of will and intellect” to the authority is the same as accepting the results of that authority in complete acceptance and obedience. The current pope has made several references to the need for obedience within the church, but a number of theologians (and a few bishops) have noted that acknowledging and demonstrating respect for the authority does not, in and of itself, require one to simply “believe because one has been told to believe.” It can be, of course, a fairly rancorous discussion.