Why is Gnosticism loathed so much?

As I understand it, gnostic communities (e.g., Cathars) were peaceful, moderate, empathetic towards women and animals in a time when such a thing was uncommon, and believed that the widespread and unavoidable misery and suffering in the world is best remedied by voluntary extinction by means of not procreating.

Am I misunderstanding things, or is that literally the reason that the Catholic church and others (as well as your average normie and /pol/tard) hate them so much?