Earlier quoted context omitted.
Decentralized exchanges exist for the more sophisticated cryptos (e.g. Ethereum).
Sure, but you will never be able to get out fiat currency from a decentralized exchange (which is what most people want).
The whole idea of cryptocurrency is that one day you won't need fiat because all txs will be happening in crypto, so not exactly a dealbreaker for the concept. In fact, it kinda proves the concept – when fiat is involved, you need middlemen. With pure crypto, you do not.