I'm not sure about FC and linkshell, it's probably something to do with not bitching about players in your party behind their backs, I dunno., but you can't use glamours because it's extremely unfair to run in looking like you're in i30 gear when you're actually in i100 pvp gear and wasting the first several seconds of the enemy's attacks as they realise you're MUCH more durable than they thought. That would just not be fair.