If you treat email as if it were a postcard that anyone can read, and you don't provide information on the interwebz that you wouldn't be willing to shout out on a street corner (SSN, credit card number, etc..) you're good. If you think any online security is actually secure against a dedicated attack, you're going to get pwned.
If you're less concerned about "security" and more about "freedom of speech", the same rules apply. In this day and age, if you say something (via postcard, on a streetcorner, on the phone, or via the interwebs) that pisses off someone with power, all I can say is send my regards to Gitmo and assume the position, because you will be fucked if it tickles their fancy to do so. If they decide to dig up stuff on you, they'll find it, encryption be damned.
There is nothing especially new about this - people who say things against the authorities out loud historically often met bad ends. The only difference these days is that many people are happily entering that data into the internet database and greatly simplifying the work the government has to do to identify and track them. If you think security through obscurity works, well, you're assuming that the government would be unwilling to scoop you up and 5 or 10 innocent bystanders.