I'd say that fine tuning your deck in casual mode would be much less effective than playing ladder. there will be much more non-competitive decks there and therefore you wont be able to see your "fine tuned deck" 's performance against other meta decks as much. you wont get useful information against meme-deck players when you are trying to play S-tier deck there.
so yes I am on the side with the OP here. I think people should not play with top tier meta decks there. that Mike Tyson example was brilliant too :D but yeah you cant (and should not) force people to play what they are going to. one can only wish, nothing else.