Saying that bitcoin isn't scarce because someone could fork the blockchain is like saying that gold isn't scarce because everyone in the world could suddenly agree to start using silver instead.
Limited resource physical commodities vs. a few bytes on your filesystem? This is a ridiculous comparison.
But what people mean when they say you could fork libcoin or something like that is not that Bitcoin isn't scarce. It's more along the lines of "We are in no way beholden to this psychotic black market pyramid scheme currency. We can just start anew with a better dispersement/capping scheme."
