Earlier quoted context omitted.
I agree about some of your points, but I don't believe that you have any reasonable expectation of privacy when emailing a person you have never communicated with before or that they won't republish your emails without first gaining your permission (IANAL).
I don't know about in the US but in the UK it's certainly the case that there's a default expectation of privacy.
I've found various opinions on-line from UK-based commentators suggesting that if an e-mail isn't explicitly marked or otherwise understood to be confidential, and it didn't contain any sort of privileged information or information that would normally be expected to remain private, then it wouldn't automatically attract protection under any privacy law. Most of these related to an individual republishing messages send on behalf of a corporate body rather than the other way around, though.