Cruelty is the act of being cruel. That is to say, needlessly unpleasant. Torture is cruel. Waving Bleeprin at Agents who've returned from Smutfic and then not giving them any is cruel. Volunteering your partner to work in continuua inhabited by their Lust Object is cruel.

The PPC are against cruelty to Canon characters, but right alongside cruelty to Mary-Sues