Which is to say that
reductio ad absurdum argument doesn't work in either direction. I think that many people reasonably base their decisions on how the table plays, and that the "metagamer" has a particular valence with many tables as someone who uses information not known to the character to impart an advantage to their character. Why would I say this? Because this is a not uncommon definition-
"We all metagame once in a while. After all, even if our characters don't know exactly what that orb with the eyes is, they've got the feeling that it's dangerous and probably shouldn't be charged head-on. But this guy seems to have read (and memorized) all the monster manuals and the published adventures, and is impossible to catch off guard. Once he sees that beast charging him, he immediately breaks out the creature's one weakness."
From TV Tropes. See also-
"It should probably be noted that the term "metagame" is also used pejoratively when it comes to Tabletop Games and other roleplaying games that expect players not to jump In and Out of Character. Here, using The Metagame is often considered somewhat akin to cheating, since it's information that the player's character couldn't possibly know (since the character doesn't know he's in a game), and shouldn't be making use of."
From "metagame" in TV Tropes.
"In role-playing games, metagaming is an "out of character" action where a player's character makes use of knowledge that the player is aware of but that the character is not meant to be aware of. Metagaming while taking part in relatively competitive games, or those with a more serious tone, is typically not well received, because a character played by a metagamer does not act in a way that reflects the character's in-game experiences and back-story."
Wikipedia
You can look here for tips on how to "solve" metagaming-
https://roleplayingtips.com/gm-techniques/how-do-you-prevent-metagaming/
From all geeks rejoice:
"The biggest reason this term gets such a bad reputation is that it generally causes issues for the DM while also killing the immersion for the other players."
So this is an unusual debate in the sense that some people are not just trying to offer their solutions for metagaming (which can include ignoring metagaming and/or offering post-hoc narrative justifications), but imposing their belief that metagaming is everyone else's problem exception for the metagamer. Which seems contrary to the vast majority of experience I have had, and is in accord with the information and advice I can find elsewhere.
Reasonable debates can be had about the way everyone needs to accept and use the metagame (for example, at most tables, the party tends to stick together and help each other, because the PLAYERS want to have a fun and cooperative game). There are reasonable debates about the extent of character knowledge (in your world, how common is the "trolls and fire" thing). There are reasonable discussions that can be had over the best way to handle metagaming, and how individual tables chose to deal with it; to extremes would be Aaron's (permissive) and Max's (not permissive).
But fundamentally, people are talking past each other, as [MENTION=6857506]Harzel[/MENTION] points out.