Ah, the "all history is propaganda" argument. Or one variant: Catholics are so dominated by superstition and so generally out of control that they simply are unable to look at facts without prejudice or to make a serious and fair argument.
THen all that's left if for us to stick out our tongues at each other, while a feckless and impotent truth goes a-begging.
One of the members of my parish, which is the Catholic Parish associated with the University of Virginia, no mean school, is a historian. He reports that one thing that prompted his conversion was that, as Protestant he began looking into "the Inquisition" (as though there were only one inquisition -- that's the first popular misconception) and found that most of what he had been led to believe was certifiably false.
Naturally he bagan to wonder why, if Protestantism is true and Truth is stronger than lies, there would be so much falsehood promulgated about history. Next thing you know, there he is, kissing the Pope's toe.
Much better for ANY and ALL sides to work hard to find the truth.
A problem with sub-conscious Manicheanism is that it is too easy to slip into thinking that victory is more important than truth.