I've been skimming through the book Faith, Reason, and Earth History, by Leonard Brand, department chair of biology at Loma Linda University. On page 266 he offers lists of evidence supporting what he would call the competing theories of natural history, "Intervention and Catastrophism," versus "Megaevolution and Neocatastrophism." His argument is that there is strong evidence for both theories, and that neither offers adequate explanations for the evidence that supports the other theory.
As far as I can tell, Brand is considered a respectable scientist and expert in the fields that he is discussing. This would be evidence to me that one could have reasonable doubt about an ancient Earth. Conclusive evidence? No. But enough to reject James McGrath's sweeping accusation that ALL YECs are liars and deceivers.
Since I'm not a YEC, and since I don't have a passionate interest in trying to decide which view is correct (and according to Brand, the evidence is inconclusive, anyway), this is as far as I feel I need to go to discount McGrath's view. Now back to things of more interest to me.