Well you can run your own mail server if you must (an absolute nightmare even if you know what you're doing) and set up pgp with all your co-conspirators, then use k9mail or another desktop client with pgp support to at least automate the cryptography. But short of that a service that makes at least a plausible privacy claim is better than one that doesn't. Until demonstrated otherwise protonmail and similar options are a clear improvement over google, yahoo, microsoft, etc and not hard to get going with.