This requires a model of the poster that not everyone reading comments will have. That can be solved by downvoting such posters to indicate their untrustworthiness.
But as I said humans are not perfect Bayesian reasoners and are not good at adjusting for unreliable speakers. We almost always either adjust too far and reverse stupidity or don't discount enough and let cherry picked sources or skewed interpretations sneak into our brains. We'll update without even noticing.
humans are not perfect Bayesian reasoners...
This seems like a selective application of a universal objection. "We almost always either adjust too far and reverse stupidity or don't discount enough," makes your reason technically not a universal objection, just an objection to learning anything from badly biased people, but this might be a confabulation added to the universal "humans are not perfect Bayesian reasoners".
I wanted to bring attention to two posts from Razib Khan's Discover magazine gene expression blog (some of you may have been readers of the still active original gnxp) on the polemic surrounding Pinker's The Better Angels of Our Nature.
Relative Angels and absolute Demons (and the related But peace does reign! )
I generally agree with some of his arguments, but found this quote especially as summing up some of my own sentiments: