So if we see someone blatantly doing something stupid, wearing the wrong gear (can't tell you how many times I've gone into AK only to see the PLD wearing the LNC/DRG gear from there) are we supposed to let them continue doing that?

Not going to lie, when I saw the PLD wearing the LNC/DRG gear (which has less armor than his AF gear) i nicely asked him to switch gear. After a few times of him acting like he was a know it all (clearly you're not since you are wearing the wrong gear) i told him "fine go ahead and wear it but i'm not healing you at all" once he died and changed gear all was well.

My point is sometimes you've gotta be 'tough' on people to get a point across and if a DPS, tank, or healer just can't understand basic mechanics of a dungeon or their class then they NEED to go.