It is not a sin, for we have a concrete example in Holy Scripture. Peter, the first Pope had some inconsistencies at Antioch and had some disputes over the law of Moses regarding circumcision. Some people from Jerusalem come down to Antioch in Syria, where Paul is ministering, and they say that without circumcision you can’t be saved.
Then after he records that incident, he says in Galatians chapter 2, he says “But when Peter came to Antioch I opposed him to his face because he was clearly in the wrong.” Peter may not have proclaimed a heresy but I would like to point out his ambiguous behavior towards the Gentiles regarding their necessary participation in circumcision. Some people came from James, he used to eat with the Gentiles; but when they came, he began to draw back and separated himself, because he was afraid of the circumcised.
We have multiple examples from the history of our Church where saints publicly admonished the incorrect behaviors of the Pope. St. Catherine of Siena who repeatedly wrote to the Popes, it may have been done privately, to return to Rome and stop this political nonsense of the Petrine office. I would imagine if St. Catherine lived during this time, she would have been writing on the internet, which is the public domain. Therefore, we can publicly criticize the Pope and the Bishops but we have to do this out of love. This is important because, according to moral theology, fraternal correction would fall under the virtue of charity.
Therefore, if my critic is not inspired and moved by genuine supernatural love, then my critic has committed a grave offense in God's eyes. It must be motivated by genuine love, first for the person and then for his position, as criticizing someone in a hierarchical position within the Church is not the same as correcting a brother or friend on a fraternal level.
Because we are not Protestants, we must submit to the hierarchy of the Church. God formed our hierarchy, and the Pope, Bishop, and Priests are divinely established positions that are constituted in a manner that represents Christ the High Priest.
As a result, we must treat it with the highest reverence because it stands for something greater than ourselves. Let us not be too critical that it is only seen as a sinful matter, but we need to take into great consideration its meritorious contributions towards the reformation of the Church.
Dear visitors of Gloria Dei and all who have already written or who will write a personal message to me. I am grateful for your attention, your kindness, for your spiritual support and especially for your sacrifices and prayers for me. God may reward you!