The point of certificates is not to encrypt the traffic, but rather to verify that the server you are talking to is who they claim they are. The server showing you their certificate is like you logging into an SSH session, which I've been doing for a long time with a certificate as well, actually.
In my browser it is either/or though. I can have encryption and verification, or none of those. Technically it would be feasable to have encryption without verification, and thus without CA's. Why isn't that an option?
You can do what you want by creating your own self-signed certificates. It's not that hard, just a couple of openssl commands. Browsers will throw up a big scary warning that the certificate can't be verified (as you'd expect), but most browsers let you click through that warning, and you get encrypted but unverified traffic.
More specifically, because encryption without verification allows for MITM and other chosen-ciphertext attacks which trivially break the confidentiality provided by the encryption.
Encryption needs entity authentication (verifying who you're talking to), data authentication (verifying that the ciphertext has been created by one of the parties in the communication), and a cipher to provide confidentiality in practice.
