This shouldn't come as a surprise to anyone. You're using a web based email service and you're sending postcards when you should be sending letters. Both this and Lavabit feel like distractions.
2. You are assuming that everyone understands that email is like a postcard.
I have even met technically competent people who were surprised to discover how easy it is to forge email headers. When even people with years of accumulated knowledge about computers carry bad assumptions around, what can you expect out of people with little-to-no understanding of computers? For a lot of people a computer is a magical box that is beyond their comprehension.