Because your link doesn't work. Why would you post something like this without verifying what Barton so approves of here? Any idiot can look on the web and find that deism has very little to do with atheism (aside from the fact that both normally believe that coming to religious beliefs is the result of a logical process). In fact, deism might well be the thinking man's counteratheism. But you'd never know it from this tripe.
He doesn't answer email - I know that from first hand experience. David Barton is also our Republican Party Vice Chairman in Texas (and a rather lousy one at that - he's in it for self promotion and to sell his videos, not getting our candidates elected). Whenever there's an internal party election going on he pulls out his self-purported "Founding Fathers" expertise and twists a bunch of out of context quotes together to portray his favored candidate as the "candidate of the founders vision" or some such nonsense. Anybody who opposes him similarly gets labelled "anti democratic" and opposed to the "Founding Fathers." I've sent out challenges to the content of his letters several times including to that address and they never respond to anything. He has no public address at the Republican Party website either.