The difficulty is in how to keep them available to end users while keeping them unavailable to malware and bad actors who post "helpful" advice or publish temporarily useful addons that get updated to malware.

I'm not disagreeing with you, but the right mechanism is not straightforward to figure out, and you'll always be in a game of cat and mouse. One that sucks resources from whatever other useful stuff you might be spending your (or Mozilla's) time on.