Whether or not people understand encryption doesn't change how well it projects them. The difference between "encrypted" and "unencrypted and not evil" is like the difference between a car with airbags and a car that has a little sticker on the dash that says "Try not to crash."
Obviously, no security is perfect, and given sufficiently evil central repository you'd still end up a situation of mistrust. But rather than take a chance with my private information simply because the people holding it tell me they aren't evil, I'll take responsibility for my own data and do my best as a user to make the right choices about how to treat that which I desire to keep private. If that means being picky about what I share/post, that's fine. If that means I need to run my own host and control access myself, well that's the burden I can choose to take to give me the peace of mind I'm looking for.