There are objecting that what Facebook is getting into is not decentralized and hence can not even be called as genuine cryptocurrency akin to what we see in Bitcoin, Ethereum and the rest of the gang.
cryptocurrency is a currency that is based on cryptography, it doesn't have to be decentralized. but when a cryptocurrency is centralized you can no longer compare it with bitcoin.
by the way Ethereum is also centralized not as much as a company coin like Facebook coin but still centralized.
Well, I agree with this statement. Bitcoin is a pioneer cryptocurrency.
So, I think it's very difficult for ALTCOIN newcomers to compete with the popularity of Bitcoin.