[hf]

The situation with beginner-friendly SSH tutorials is, in a much lesser degree perhaps, comparable to the crypto texts: Good will alone does more harm than good.

This treatment ssh does not mention ssh-agent and, more importantly perhaps, implies that there is a certain virtue in having private keys unprotected by sturdy passphrases lying around.

There is not; most emphatically not.

[voltagex_]

Hypothetically, if one was reading this article and had a large number of unprotected private keys around, one could change the password on these keys by issuing

   ssh-keygen -f id_rsa -p