Depends on the situation. An anonymous person contacts you - how do you get their key from a public authority? There is no impersonation attack possible in thi

Depends on the situation. An anonymous person contacts you - how do you get their key from a public authority? There is no impersonation attack possible in this case. Someone claiming to be Edward Snowden contacts you today (now that he is longer anonymous) - in this case yes, the author just including their key would not necessarily be secure.