What are Catholic extremists and what do they do?

Answer 1

A Catholic answer (Catholics in union with the Pope)

It can be difficult to know exactly what "extremist" means: To borrow a formula: one man's "extremist" can be another man's "devout adherent."

Perhaps it might be said that we move from "devout adherent" into the territory of "misguided adherent" or "extremist" when we find persons more devoted to their own wrath, vengeance and a spirit of tribalism than to any benevolent deity. Understood in this sense, I suppose Catholic extremists would behave in a way comparable to the manner in which misguided extremists who are adherents of other faiths behave - that is, having had the misfortune to become filled with a spirit of pride and wrath, and an attitude of tribalism, and, having departed from the humble service of God, while yet clinging to the external trappings of His service, these individuals offend God by committing myriad offenses against their neighbor, particularly sins against charity and justice. These sins might include detraction, slander, all the way to murder. Meanwhile, these individuals deceive themselves that they act righteously, which is all the worse for them, since self-deception makes terribly remote the likelihood of repentance.

I would hasten to add that this sad condition described above would be by no means the exclusive provenance of Catholics. Unfortunately, members of other Christian churches, as well as adherents of other religions have fallen victim to the same condition.

ANSWER:

I would add that atheists, agnostics are also no stranger to extremism. Atheistic Communism is certainly extremist.