Strictly speaking, a heretic is one who causes divisions in the church by teaching an aberrant doctrine in an attempt to draw followers after himself. A person who privately holds some views or entertains discussions on issue not considered orthodox is not a heretic until he becomes divisive about it.
What is heresy? One definition would be a doctrine that has been condemned by a council. The Fifth Ecumenical Council is often thought to be a condemnation of universalism, because it condemns the teachings of Origen by name. But the specific issue was Origen’s belief in the preexistence of souls; it was his belief that these souls would be restored to their original state that was condemned by the council.
The Council never condemned universalism universally, in all its forms. The Council never mentioned Gregory of Nyssa who taught a form of universalism but whose theology was otherwise orthodox. In fact Gregory is still considered on of the greatest fathers of the church. (See Robin Parry’s discussion)
On the other hand, the council of Orange specifically condemned the teaching that God predestines anyone to evil:
We not only do not believe that any are foreordained to evil by the power of God, but even state with utter abhorrence that if there are those who want to believe so evil a thing, they are anathema.
Historians say this statement was specifically directed toward those who teach “double predestination,” i.e., the belief that some have been ordained by God to reject his grace. They of course did not condemn Augustine by name even though many believed this was implied by his teachings. Otherwise the council of Orange fully supported Augustine against Pelagius.
Still, by the standard of church councils, we have to admit that universalism per se has never been condemned as heresy, but the doctrine that often passes by the name of Reformed theology has been given the official anathema.
Ernest Tubb, Hank Jr., and others had a country song a few years back, “I Guess We Should Have Left Him Alone and Let Him Sing His Song.” One line keeps ringing in my mind (it sounds better when I can hear the tune),
If we don’t like the way he sings, who’s gonna cast the first stone?