Indeed, that argument is utterly stupid.
First of all, if he receives an encrypted email from a stranger, this is because he has a GPG key, too. So that stranger had every reason to assume that he's also a "GPG tinfoil hat".
Sarcasm aside, using GPG for minor stuff is not about paranoia, but about protecting minorities! This includes discriminated minorities as well as whistleblowers, investigative journalists, and so on. I for myself may not need that level of protection, but others do. Maybe even the stranger I'm writing to. The more encrypted communication we have, the less minorities spike out who really need that protection.
So encrypting everything is not "I fear", but a political statement. And that political statement is simply "I want encryption to become the norm rather than the exception, to protect minorities".