If you replicated the brain, you'd be
replicating the sense of self. Which is why there'd now be two. The sense of self doesn't come from nowhere; it comes from the brain.
The same is true of the brain. Prior to its actual existence, the particles that made up that brain could have been
anything.
That doesn't mean there's an infinite number of potential brains, though.
To show that the senses of self are infinite while brains aren't, you have to show something that's
different about senses of self, that
isn't true about brains. And no, the fact that the sense of self is more like an action (like running or spinning) than a physical thing doesn't get you there. Actions don't happen without an actor, and senses of self don't happen without brains.
Once again, Jabba, the key is
physics, not mere biology. Two identical brains may be biologically the same, but they occupy different
physical locations, which is why they're distinct. But there's only a finite number of physical locations in the universe.
Physics!
Physics!
Physics!
eta: I seem to have stopped being LCP again. Oh well, no way of telling how these things work!