I think we end up with a singleton no matter what, and it's only a question of whether we choose the singleton, or try to maintain an impossible balance of power and thereby fail to control who builds it. Once it's possible to replicate directly using only computational resources, murder becomes an instantaneous and massively scalable means of reproduction. And once that's true, it just isn't possible to have any semblance of a balance of power; either someone takes over the world, or someone destroys the world accidentally while trying to take it over.

My perspective as a programmer (not specifically focused on security, but definitely not a layman), is that computer security won't ever be good enough for those circumstances, no matter how many resources are thrown at it, and that throwing resources at computer security is only a mixed blessing anyways.