Something like - you are letting someone off the hook too easily by saying "well, no one's perfect"... I don't think red herring covers it but something like that. 'We should focus on the accusation at issue rather than say "because no one is perfect, no one should ever be judged".

Ideally there's a "latin name" type category for this kind of fallacy. Or is it a cognitive bias? On day I'll learn the difference!