Jeffrey Shallit surveys the press coverage of books on atheism and wonders why atheists are always described as “militant”:
From the meaning of “militant”, you might expect that Dawkins, Harris, and Hitchens are burning down churches, or at least leading protests, stirring up crowds with their fiery rhetoric. You would be disappointed, of course. What Dawkins, Harris, and Hitchens have done is write books. Hitchens is more of a curmudgeon than a militant, and Dawkins and Harris are both rather mild-mannered. Nobody is leaving their public events carrying torches and singing the atheist analogue of the Horst Wessel song.
Over at Pharyngula, Jurjen has an historical explanation for the origin of the term. Of course this doesn’t explain why “militant” is always used with public atheists and rarely with (far more militant) advocates of religion.