Besides, symmetric schemes tend to perform better. Hence the idea of using a public-key scheme like DH for key exchange and then switch to symmetric crypto like

Besides, symmetric schemes tend to perform better. Hence the idea of using a public-key scheme like DH for key exchange and then switch to symmetric crypto like AES. Always avoiding public-key isn't really possible unless you have some sort of secure channel to agree on a key for some communication. But then again, if you have that channel, you might just as well communicate through that. When encrypting files locally though, there is absolutely no reason I can think of to use public-key cryptography.