"[There is] a rather unlovely asymmetry in public discourse...one that is generally on display whenever scientists debate religious apologists. For instance, when a scientists speaks with appropriate circumspection about controversies in his field, or about the limits of his own understanding, his opponent will often make wildly unjustified assertions about just which religious doctrines can be inserted into the space provided. Thus, one often finds people with no scientific training speaking with apparent certainty about the theological implications of quantum mechanics, cosmology, or molecular biology.
This point merits a brief aside: while it is a standard rhetorical move in such debates to accuse scientists of being "arrogant," the level of humility in scientific discourse is, in fact, one of its most striking characteristics. In my experience, arrogance is about as common at a scientific conference as nudity. At any scientific meeting you will find presenter after presenter couching his or her remarks with caveats and apologies. When asked to comment on something that lies to either side of the very knife edge of their special expertise, even Nobel laureates will say things like, 'Well, this isn't really my area, but I would suspect that X is...' or 'I'm sure there are several people in this room who know more about this than I do, but as far as I know, X is...' The totality of scientific knowledge now doubles every few years. Given how much there is to know, all scientists live with the constant awareness that whenever they open their mouths in the presence of other scientists, they are guaranteed to be speaking to someone who knows more about a scientific topic than they do."
My thoughts on why atheism is not arrogance: