People generally have their feet set in cement and cannot be reasoned with. It is therefore my view that we should simply say what we think and bring our evidence to the table.
That’s why I admire people like Chomsky, the late Gore Vidal, and the man above, Norman Finkelstein. They say what they believe to be true and defend their position with vigor. They are not nice, because like every other means of persuasion (short of advertising and propaganda), being nice does not work. Knocking an opponent for a loop can remove cobwebs, creative cognitive dissonance. Honest people then self-reflect and alter their views.
It is rare but it happens.
By the way, Norman Finkelstein is banned in the State of Israel. He cannot enter the country. If he were nice (i.e., stfu) that would not have happened.