The Post reminds us paranoia can be quite rational:

"People from North Korea are very paranoid," said Kim Heekyung, a clinical psychologist at Hanowan [in South Korea] who supervises group therapy for defectors.  Paranoia, she added, is a rational response to reality in North Korea.

A new U.N. human rights report describes North Korea as a place where ordinary people "live in fear and are pressed to inform on each other. The state practices extensive surveillance of its inhabitants. . . . Authorities have bred a culture of pervasive mistrust."

When defectors arrive at Hanowan, they whisper. They are reluctant to disclose their names or dates of birth. They question the motives of people who want to help them. They say South Koreans look down on them. On field trips from Hanowan to get their first checking accounts, they find bank tellers to be terrifying. …

"Paranoia in North Korea helped people survive, but here in South Korea, it is an obstacle to assimilation," Kim said. "Many defectors are scared to do anything."

Our problem isn't a capacity for paranoia, but is misreading clues about when to invoke that capacity.   We say someone has a mental problem if they are more paranoid than we think makes sense in our society.  But of course personal circumstances will vary, so we should beware of overconfident paternalism in judging when others are excessively paranoid.

Among North Korean defectors the opposite mental problem of insufficient paranoia is probably more common.  Alas we don't see many of those folks for obvious reasons.