Does that mean I have to stop calling CM and fk formal heretics who will surely burn in hell?
Wow, this is such a tricky question.
explicit formal heresy: I know that the Catholic Church teaches such-and-such but I don't believe it anyway. This kind of heresy is formal precisely because it undermines the very formal motive of faith, the teaching authority of the Church. I've never met a Traditional Catholic who falls into this category. Why is it that we do not have various groups among Traditional Catholics arguing about whether Jesus rose bodily from the dead or whether Our Blessed Mother was immaculately conceived?
implicit formal heresy: Now, it's certainly possible for a person to PROFESS adherence to the Church's teaching authority and yet be a heretic. So for instance the Church condemns an opinion as heretical but you remain obstinate in claiming that it's not. Ironically, CM and fk, the chief culprits in denouncing others as heretics, come the closest to this due to the fact that their position implicitly undermines the magisterium and subjects all truth to their own private judgment.
explicit material heresy: Usually comes from raw ignorance. I don't believe in the Immaculate Conception because I think that the Church's teaching refers to the conception of Jesus. Such a person immediately rejects this opinion when it's explained to them that they're in error.
implicit material heresy: Theological conclusions or positions improperly deduced from Church teaching in such a way that they implicitly undermine dogma, i.e. if taken to their logical conclusions.
Then there are other errors which fall short of heresy.
I think that it's perfectly OK to argue that someone might be in material heresy.
So how does one know that someone appears to be accusing others of formal heresy? Well, the "you're going to burn in hell" or "you're not Catholic" comments are usually what tips their hand.
Now, ironically, in declaring other people outside the Church for holding to implicit material heresy, one can become schismatic. Home-Alonism probably implies schism.
Now, the arguments we've had with CM and fk revolve around the implicit vs. explicit heresy distinction. CM and fk are adamant that the denial of their theological conclusions involves explicit rejection of Church teaching, while I argue that it cannot be more than implicit, since there's no explicit Church teaching, for instance, that "If anyone believes in Baptism of Desire, let him be anathema."
Of course, even CM and fk have stated that they believe people could be only materially heretical.
So, for instance, I argue that sedevacantism might be implicitly heretical, but I do not accuse sedevacantists of heresy. If anything, the dogmatic sedevacantists are schismatic for their effective excommunication of all those who disagree with them. In the case of priests, refusing sacraments to people who hold contray opinions would also tip their hand in terms of asserting that those people are heretics and not Catholic.