This is true of any conversation, but perhaps applies to political debate more than anything else, especially given the vitriolic days we live in. The most dangerous thing anyone can do is to imply that their opponent is less than human. It is what births the impulse that translates to murder. Your conscience will give you less trouble if you accept that the person you disagree with is somehow less capable of love, less capable of empathy and more given to animalistic tendencies.
Unless you accept your opponent as an equal, unless you come to terms with the fact that the other person has reasons for being the way he is and for saying or doing the things that he or she is saying and doing, you will, at least in theory, be in the same category as the devils you seek to defeat.