I think there is a word missing from the post you addressed: "If you believe in a common ancestor but say you don't for fear of some punishment, what does that make you?"
I concur with the stronger definition of liar, entailing purposeful deception. In the case of human beings the capacity for self-deception is tremendous. The capacity to avoid speaking what is true is even greater because we fear the consequences. Our "common ancestor" was a liar and a murderer, so it is no stretch in view of the ultimate destination of the flesh we currently inhabit, to consider ourselves at least similar.
Meanwhile, it would be easy for science to confuse a common Creator for a common ancestor. From a purely physical standpoint the two are not much different. The argument concerns history unvailable to any current observer, and so to a large degree the charge "it's not science" applies equally to those who assert an intelligible universe came about without the aid of intelligent design.
WTF? placemarker