Heresy was always false, but not necessarily always heresy
Lately, having had contact with many new people who are interested in the Catholic Faith, I have also been presented with new attacks on the Faith, which certainly call for an answer. There is nothing more insidious than when the Catholic Faith is attacked by those who would claim to love it and hol
d it more dearly than anything else, for who would suspect them of being wolves?
We know since the Councils of Florence and Trent that it is a Divinely revealed dogma that heretics have always been able to baptize validly, if they used the correct matter, form and intention. But does that mean that it was always heresy to disbelieve this? No it does not mean that - there WAS a time when a person could lawfully believe that heretics could not baptize anyone at all, even though that proposition later was condemned under pain of anathema.
The other example from history is Pope John XXII, who in the middle ages taught a doctrine that would later be condemned by his successor, Benedict XII. But if he was a heretic, why was he never declared an antipope? Because it was not heresy to hold contrary to the doctrine that would be declared by Pope Benedict until AFTER the Church, by his decree, had proposed it as Divinely revealed. Does that mean that Pope John was right, or that the doctrine was not contained at least implicitly in the Deposit of Faith? NO! Benedict XII did not make up a NEW doctrine that was alien to the Church, but rather he clarified a point of revelation that had not yet received attention from the solemn Magisterium, since it only became a matter for controversy after the confusion that followed Pope John's erroneous public teachings on the matter (in which he specifically stated he was NOT intending to make a dogmatic definition, but was only proposing his personal theological opinion).