CONTRADICTION

Antisthenes
We must not contradict, but instruct him that conradicts us; for a madman is not cured by  another  running mad also.

Johnson, Samuel
Assertion is not argument; to contradict the statement of an opponent is not proof that you are correct.

Richter, Jean Paul
We take contradiction more easily than is supposed, if not violently given, even though it is well founded.—Hearts are like flowers; they remain open to the softly falling dew, but shut up in the violent downpour of rain.