“If the credibility of Religion Forum posters were subject to personal attack, then the advantage would not go to any particular religious belief but to atheists...”
No, the advantage would go to the truth. And that would be very good for Catholics. Disadvantaging the truth is anti-Catholic.
“...because not just the statements would be subject to empirical or logical proofs but the poster himself would be subject to accusations of malicious intent, superstition, mindlessness, etc.”
In that Catholics are regularly accused of all these things, in general, I'm not sure that it would matter much to say them in particular. But the things you mention are all subjective in nature.
There are objective facts that exist about posters that are observable by all, and these facts can be used to impeach the credibility of a poster. Disallowing them is disadvantaging the truth, and to disadvantage the truth is inherently anti-Catholic.
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