I encourage metagaming too, but more in the sense that I want characters to get along because their players are IRL friends, not because the characters themselves should naturally get along and stick together. Similarly, I like when players to actively seek ways for their characters to get aboard the adventure even if logically, their characters would likely do otherwise. Otherwise, I prefer when the characters get to discover their world and adventure independently from player knowledge. Heck, I even narrate prologues and epilogues where the bad guys are revealed doing things the PCs have no way to know (yet).
But I think there’s a lot of information that should be relatively well known in the gaming world. Things like killing werewolves requires silver weapons, vampires cannot withstand sunlight, trolls regenerate if not burnt, red dragon breathe fire, etc. These should be present in nursery rhymes and children tales.
As a DM, I also sneak false information from NPC as people are often misinformed or else folklore has deformed truth. Things like dragons acquire different breath weapons with age, vampires are repelled by garlic, mundane prayers will protect you from demons, etc. More often than not, my players are aware of these falsehoods and I leave it up to them to decide whether their characters know it. In doubt, they usually seek someone who would know…
A healthy level of metagaming is required IMO, but I wouldn’t go as far as PC knowledge = player knowledge personally.