Comment 6 by CEVA34 :

If every word in the Hitchens paragraph is true, it makes no difference to the validity (or otherwise) of the Mencken paragraph, does it? If we suddenly discovered Darwin was a serial killer, would we abandon the Theory of Evolution? If Hitler said two and two make four, would it not be true? What's the phrase? Ah, I remember - ad hominem.

I don't think you're being fair. Hitch's criticisms of Mencken do not amount to an ad hominem attack.

Ayn Rand, and Karl Marx, were atheists, but they also were profoundly wrong about a bunch of other stuff. Just because Mencken was an atheist does not mean he was not profoundly wrong about a bunch of other things.

Criticizing a writer based upon the writer's actual words and ideas is playing fair--and it is wise to bear in mind that just because someone got something like atheism correct is no reason to assume they got anything else correct.

Atheists are already falsely accused of effectively worshiping their favorite writers, and your attempt to equate fair criticism of a specific atheist with an ad hominem attack on that atheist merely reinforces the incorrect perception that atheists are over-eager to engage in hero-worship in lieu of more traditional forms of worship.