I can give you my public key and you can verify my messages.
Hrm. I would have answered, "how do I know a man in the middle didn't give me
their public key instead?" But the same weakness exists with CAs. How do I know a man in the middle didn't add their key as a CA when I downloaded my browser?
It's tricky.
...I wonder if people still use Namecoin.
LOL, no doubt. And while there have been instances of CAs behaving badly, SSL is still used and generally trusted for transactions and communications of low to moderate importance.
For example: you're using it right now.