Maharal, Be'er Ha-Golah 5:1 (translation/adaptation by R. Yitzchok Adlerstein):
Just as love often causes you to overlook deficiencies, hatred can make you discover imagined faults, and summarily dismiss other viewpoints. This is a consequence of a jaundiced eye and a warped mind. Even th great secular philosopher wrote about how inappropriate it is to contemptuously dismiss the position of your opponent in order to shore up your own position. The truth is the best defense against the barbs and criticism of your enemies. Producing clear evidence is the necessary and sufficient refutation of your adversary's position.(emphasis added)
In addition, your arguments will have far greater appeal to people who truly seek the truth when you calmly and rationally consider your opponent's position, rather than dismiss it with contempt and hatred. You will protect yourself from the accusation that your arguments are self-serving, rather than a serious attempt at truth.
You should not provoke your adversary to anger, or show hatred to him, but show compassion, conceding his correct points, and speak softly and calmly with him... Disputants should show the same courtesy and udnerstanding to each other as they do to themselves; it is never appropriate to strong-arm your adversary into submission.