They could have started fresh like the zillion other cryptocurrencies that have started up since 2009, some of which appear to have real value. You wouldn't look askance at those, at least from a healthy-market perspective. The only difference here is they distributed initial currency fairly perfectly to the best possible audience of Bitcoin fanatics -- without a single spam email!
Cloning a company makes no sense in the physical world. But when it's a purely digital asset, it can be copied very cheaply.
Why isn't this zero-sum? Because it increases the TAM, rather than competing with its doppelganger in a saturated market. Maybe one ends up killing the other, but for now there's room for both.