Calvin on polemics

"That bitter reproaches and scurrilous witticisms are unbecoming in Christians, both sides agree. But as the Prophets did not refrain from derision, and our Saviour himself speaks in cutting terms of perverse and deceitful teachers, and the Holy Spirit everywhere inveighs will full freedom against this class of men, it is thoughtless and foolish to raise the question, whether it be lawful gravely and sternly to rebuke those who expose themselves to shame and disgrace; for this is to bring a charge against the servants of God, whom holy zeal often impelled to harsh and bitter speeches. No doubt every individual is always bound to look well to the cause from which he either takes fire or speaks keenly."

Calvin's Tracts Trans. Beveridge Vol 2, 'Last Admonition of John Calvin to Joachim Westphal' p350