Polemics (n.) is war in suspended form: hand one side real power and you get the Soviet purges of linguistics and genetics.
Polemics (n.) is not a style but a morality — and a bad one: shut the book the moment an author calls his adversary an "infantile leftist."
Polemics (n.) that loses control of itself is a sign: people are fairly rational, so when they stop knowing what they are saying, something serious is at stake.
Polemics (n.) borrows three old costumes — the heresy hunt, the trial, the party war — and treats the other person as a heretic, a suspect, or an enemy to be wiped out.
Polemics (n.) is sterile — has anyone ever seen a new idea come out of one? — because it pushes each side to retreat to its rights and innocence instead of taking risks.
Polemics (n.) on the model of war is dangerous: treat a disagreeing thinker as a class enemy long enough, and when real war comes you may be tempted to treat him as one — that road leads to oppression.