One can argue perhaps against the necessity of Kripke.. I was just putting it out there. For example, even if I am essentially me in some way that can never be repeated, all possible worlds arguments fail as, the contingency of causality is what is necessary for a particular person to even be brought about. So though essential qualities can exist in all possible worlds, those essential qualities are contingent on time, space, and causality playing out a certain way. There was never a possible world, let's say (other than this contingent one), where my DNA would have come about, as one second later, there would be someone else born, not me.

However, the all possible worlds argument obtains in an abstract thought experiment way if we were to designate (rigidly) what it is that obtains in all possible worlds. So I still think it's useful.