In the Summa, Thomas Aquinas says that you can reason with someone who holds a different doctrine from yours so long as that person is open and searching. On the other hand, if the person persists in his view, and does not come around to the Orthodox position, it becomes a sin of willfulness on his part, and Aquinas is quite clear what is to happen in that instance (SMT SS Q A Body Para. 1/2):
I answer that, With regard to heretics two points must be observed: one, on their own side; the other, on the side of the Church. On their own side there is the sin, whereby they deserve not only to be separated from the Church by excommunication, but also to be severed from the world by death. For it is a much graver matter to corrupt the faith which quickens the soul, than to forge money, which supports temporal life. Wherefore if forgers of money and other evil-doers are forthwith condemned to death by the secular authority, much more reason is there for heretics, as soon as they are convicted of heresy, to be not only excommunicated but even put to death. On the part of the Church, however, there is mercy which looks to the conversion of the wanderer, wherefore she condemns not at once, but “after the first and second admonition,” as the Apostle directs: after that, if he is yet stubborn, the Church no longer hoping for his conversion, looks to the salvation of others, by excommunicating him and separating him from the Church, and furthermore delivers him to the secular tribunal to be exterminated thereby from the world by death.
Aquinas’s use of the word “exterminated” here is particularly chilly. Thank goodness we live in a secular age with the separation of Church and State.