In Benedict XIII's defense, his fellow, er, opposing, anti-pope, John XXIII, was convicted not only of schism, but also of heresy, simony, and immorality. And historian Edward Gibbon (not a neutral observer, I'll grant you) declared that provable charges of piracy, rape, sodomy, murder and incest, against John XXIII, were hushed up.
I don’t see how one can defend one antipope with another antipope.