A certain amount of this boils down to, "Don't be mentally ill or have an otherwise disordered mind." I've known people who were the sort of crank he's talking about, and they were generally — though not always — unhealthily isolated people who had difficulties managing their personal lives. Most had a tenuous grasp on reality, especially the motivations of other people.

There are cranks who could respond to these rules, but I believe (though I am not a mental-health professional) that many would be unable to.