The big bang is an extrapolated theory with possibly one piece of evidence: the cosmic microwave background. The CMB may be interpreted in other ways. Not believing in the Big Bang is far removed from being a young-Earth creationist. Many more things have to be wrong (perhaps logic itself) for young-Earthism to be proven right. The field of cosmology is still pretty young and the theories supporting it are much more likely to be changed. But the general idea that the Earth (and the universe) is old (billions of years at least) has many different and unrelated pieces of evidence supporting it.
I noticed that Dawkins didn't really discuss that point much; that's a matter for another, much longer, article. His thesis was simply that the orthodoxy enforcement should stop in the same place for religious beliefs as it does for non-religious ones.
Arguably, the whole article is in response to this very idea. The idea is succinctly rephrased in his article (as a third party quotation) here:
"If Gaskell has produced sound, peer-reviewed literature of high quality then I see no reason for denying him the position, even if he believes Mars is the egg of a [giant purple Mongoose]"
That's a very good question. If you haven't done so already, may I suggest reading the book Kicking the Sacred Cow by James Hogan. He deals with this question all throughout his book.
