Francis J. Beckwith wrote a First Things blog post, "On the Irrationality of Richard Dawkins," in which he argues that Dawkin's call for "reprimand and correction" against 'irrational' theists is itself irrational in the face of his own thoroughgoing atheism, since it contradicts Dawkins' readily-admitted denial of the ultimate existence of things like "duty" or "purpose".
As I read, I confess to being a little disappointed and bored with the argument. Let me play the honorary atheist here and pine that the entire post was a lengthy exercise in missing the point.
Dawkins, and I am sure most thoughtful atheists, are by now weary of the chorus of theists: "without God there cannot be anything like real meaning in life." For myself as a theist I would hope we would at least do our opponents the service of avoiding unnuanced choruses that, anyway, don't tell the atheists anything they don't already know. "The universe that we observe has precisely the properties we should expect if there is, at bottom, no design, no purpose, no evil, no good, nothing but pitiless indifference" (Dawkins in Scientific American, 1995). Of course he knows, and unless we're willing to get to the bottom of why Dawkins has no problem assigning moral duties to his intellectual peers, we haven't begun to speak to him.
Atheists, as class, are not generally nihilists, and for most of them the Christian dichotomy between "ultimate life meaning" and "absolute meaninglessness" is a false option. There's a book on that very subject, as well as a collection of infidels.org essays. Bear in mind that by linking these things I am not endorsing them; I am only pointing out that we are past the point when the charge of nihilism can be made without elaboration or nuance. Atheists, for their part, believe they have already answered that charge.
For atheists, the key argument is that the Christian false dichotomy ignores the fact of non-ultimate meaning, and it is this non-ultimate meaning which atheists argue should be enough for anyone to live for. We are nothing but mammals after all; why should we bother about eternal things at all?