when you have strong beliefs about a certain topic, knowing confirmation bias exist, gives an incentive to look closer at all the relevant statistics to see if those are biased or if your selection of statistics might be biased. once you know what's up you have better grounds to defend your belief (or possibly change it on your own) and thus prevents you from making a fool out of yourself when challenged. in short: saying "your numbers are biased" is always an option to shut you down unless you've checked and can credibly respond with "nu-uh!".
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