To purchase the coins you need to use an exchange. To sell the coins you need an exchange. Cryptocurrency isn't usable without fiat, and it's value is based on fiat.

Unless you're using very specific coins (which aren't allowed on most exchanges), your transaction history is public to the world, which is worse from a privacy perspective than fiat. If you really used coins as your primary currency, it would be pretty trivial to obtain your identity from your transaction history.