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This entire business may be pretty simple. If we have anonymity both ways, (where one or neither party knows the others physical location), then who cares about the content of the message?

You might as well send it in plain text, Except you need RSA just for the signitures so you know you aren't being spoofed.

Very good reasons. "Here is my plan to kill President Foo: ...." Just because you and your hired gun are anonymous, you don't want anyone, especially the government, to read your message. It could throw a wrench into your plans. Marc