Republic of Sophistry

(In this instance, Kavanaugh): Is he lying or telling the truth? Did he commit this crime or not?

Here are the facts we know with certainty:
He is a conservative Republican and Republican Senators want to confirm him for that reason. And for that reason, they believe he is telling the truth and did not commit that crime.
Democrats, who are generally liberal, want to not confirm him for the same reason. Therefore, they believe he is lying and did commit that crime.

Similarly, if you and I disagree about the policies of the polity, you had better have clean hands, or else you must be wrong about those policies. Unless I have dirty hands, in which case I must be wrong.