Why is it necessary for John Mccain to belittle and condesend during the Debates?

He's got nothing else. Common knowledge is that if you have something to say, you will; if you have nothing to say, you smear. You should vote for the best candidate - the one who will take care of Americans, do his best to leave the nation better than he found it, and uphold the goals and ideals of our Declaration of Independence and Constitution.