The Use and Abuse of Richard Dawkins

Brandon of the excellent blog Siris links to a post at the Intelligent Design blog Uncommon Descent, which presents the following argument (as laid out by Brandon):

(1) Atheistic naturalism is true. (assumption)
(2) One can’t infer an "ought" from an "is." (assumption)
(3) All that is is the natural world, and the natural world is all there is. (from 1)
(4) There is nothing in the natural world from which we can infer an "ought." (from 2 and 3)
(5) For any action, there is nothing from which one can infer that one ought to refrain from performing that action. (from 4 and 3)
(6) For any action, it is permissible if and only if it’s not the case that one ought to refrain from performing that action. (assumption)
(7) For any action, it’s permissible to perform that action. (from 5 and 6)

Brandon and his commenters do a fine job of showing what's wrong with this argument, but I was intrigued by something else in the U.D. post (emphasis mine):

(1) That atheistic naturalism is true.

(2) One can’t infer an “ought” from an “is.” Richard Dawkins and many other atheists should grant both of these assumptions.

Richard Dawkins is a biologist. Anyone who's read his non-biological writings knows that he is not, by any stretch of the imagination, a philosopher. So building an argument based on a philosophical position espoused by Dawkins, whatever the ultimate validity of that argument, seems like cheating, doesn't it? Why not begin with assumptions that atheists who've actually read Hume might (should? should seems ironic given the content of the argument) make?

To be fair to the U.D. poster, Barry Arrington (himself a lawyer, and not a philosopher), atheists seem to have propped Dawkins up as their spokesperson on all matters, be they biological, theological, sociological, psychological, or philosophical (the cultish Dawkins worshiping is somewhat disturbing, in fact), so I suppose they're getting what they deserve.