My initial thought was that you can only invite a new player if someone LEAVES.
meaning you can't kick someone and replace them, a player has to actually leave in order for you to invite someone else.
the only abuse I can think of that would come from this, is groups literally just sitting there and saying they wont go anywhere until the person they want go submits and willingly leaves, which is ridiculous and wouldn't happen nearly as often as if you could replace someone simply by kicking them.