Argument:
1. All men have free will.
2. The individual elected to the papacy is a man and remains a man even after ascending to his office.
3. Therefore the pope has free will.
4. Heresy is an act of the will.
5. Therefore the pope can choose to be a heretic.
6. To claim that “God would not allow” a pope to fall into heresy would mean that a pope no longer has free will.
[Source]
Reply:
1. All human persons are subject to prevenient grace, which no human person can resist. (If you’ve never heard of prevenient grace, you aren’t qualified to discuss this theological question on Popes and heresy.)
2. The Pope is a human person, so he is subject to prevenient grace, even after his election to the papacy.
3. Therefore, the Pope’s free will is NOT the only consideration in whether or not the Pope can commit certain types of sins.
4. A papal heresy would be contrary to the indefectibility of the Church; therefore, the prevenient grace of God does not permit it.
5. The Magisterium also teaches that each Pope has a never-failing faith;
6. Since heresy is a failure of faith, which in the Pope would gravely harm the indefectibility of the Church, no Pope is permitted by prevenient grace to teach or commit heresy.
7. Prevenient grace keeps the holy souls in Purgatory from sinning at all, so the same type of grace can certainly keep the Pope from sins that contradict the indefectibility of the Church. The Pope can still sin gravely in personal matters, but not the grave sins of apostasy, heresy, or schism.
RLCJ
the reproach of Christ 
O, Amis très chers,
Ces questions sont en fait plus complexes qu’on ne croit et les avis de nombreux théologiens ne coïncident pas entièrement. Ne nous permettons pas d’émettre là-dessus de jugements ni même d’avis et d’opinions péremptoires, ce serait d’_une extrême imprudence:”Rome a parlé,la cause est entendue!” Justement, cela n’est pas toujours le cas, car certains points restent encore en suspens! La chose est si délicate qu’il faut suivre le conseil de Notre-Dame de Fatima à soeur Lucie en 1931: le Saint Rosaire quotidien! Pour nous autres, cela doit suffire!
Très humblement vôtre,
Le pauvre pécheur que je sais être.
When the Pope and the Church are under attack, we must defend with dogma, doctrine, and sound theological arguments and opinions.
When a person misses a premise or has the wrong premise(s), go to the wrong conclusions.
Their first two premises are correct and thus they arrived at the correct conclusion:
Premise# 1. All men have free will. – (Correct)
Premise# 2. The individual elected to the papacy is a man and remains a man even after ascending to his office. – (Correct)
Conclusion: Therefore the pope has free will.- (Correct)
But now comes their missing link:
Premise # 1 Heresy is an act of the will. – (Correct)
Premise # 2 (?) Missing – They fail to know or recognize who this particular man, the Pope, is. The Pope is a man, yes. But we all also receive gifts from God. This particular man, the Pope, receives a particular gift that no other person receives.
Conclusion: Therefore the pope can choose to be a heretic. – (Wrong).
They missed a premise, they failed to recognize that this particular man, Peter and their successors, unlike any other man on earth, receives the gift of ‘truth and never-failing faith’ as a person in his See (Luke 22:31-23; also taught infallibly by Vatican I).
Thus, their final conclusion is also wrong:
“To claim that “God would not allow” a pope to fall into heresy would mean that a pope no longer has free will.” – (Wrong). This is explained by Ron in this post and it has to do with prevenient grace which we are all subject to.
The following includes their missing premise:
Premise # 1 Heresy is an act of the will. – (Correct)
Premise # 2 The Pope is a man who receives the gift of truth and never-failing faith from God. – (Correct)
Conclusion: Therefore the Pope cannot be a heretic, schismatic or apostate. – (Correct).
Adding to my comment above, if we go by their selected premises only, we can also arrive to the wrong and heretical conclusions that Jesus or the Virgin Mary can also choose to be heretics (since they are also persons with free will). But they are missing who Jesus and the Virgin Mary in particular are.
*In my last sentence above i meant “but that is missing who Jesus and the Virgin Mary in particular are” – Not “they are missing who…”. Just wanted to clarify that.
said otherwise, those wolves in sheep clothing who want to rip apart the church are the heretics, not the pope. Or should I say, satanists according to their actions, even if they claim they fight satan. Satan would love to see what they do. In the past, he would certainly love to see their predecessors burning people alive. Even if those deluded people were real heretics, Jesus never said they should be burned. Cardinal Sarah goes rampant against the pope as we speak. So is cardinal Burke. I wonder what would they do to the common catholics, if they had the medieval power? As a bottom line, many of us would have been excommunicated for what we are writing. Until when they will hold those respectful positions in the Vatican? Until they decide themselves to leave the Church? Even if not excommunicated, their place is not in the Vatican. I hope this holy synod will put an end of the heretics inside the walls.