I think it's a bad mistake to confuse what you're calling metagaming with the idea that it's being done to "win". You've already said there's no winning and losing, but then you're making an argument that doing this is trying to win. It's hard to follow.
Yes!
In the example I gave at the beginning, where the monster used a mind control ability, what would have happened had we acted on that player information? Well, we would have used our actions punching our companion, instead of damaging the monster (and its minions). Our charmed companion would have presumably defended himself, so attack rolls would be required, and even if they succeeded he still needs to make a saving throw...
In other words, the encounter can still be challenging, and can still be fun. (And in my opinion
more fun than the pretending we did.). Really the only reason to be bothered by the metagaming is because one thinks that metagaming is bad.
My analogy here is driving etiquette, when there's an upcoming merge. Now, every traffic flow expert will tell you that the greatest overall efficiency is achieved when people "zipper" at the last moment. But I grew up with the fervent belief, bordering on religious ecstasy, that one should attach themselves to the end of the line and wait their turn, and that only sub-human scum zip past and merge at the last second. It's not about efficiency, but protocol. Etiquette. Rules. I will go so far as to sit half in the slow lane and half in the empty lane to keep people from passing.
But, really, those people zipping past are, in aggregate, reducing congestion. So really my only possible objection is that
it just doesn't seem right.
I think that's some of what's going on with the hatred of metagaming.
If only I could be as sanguine about merging as I am about metagaming.
