You will not find any issues with inbreedig of insects. In time, you may see some higher incedence of mutations or weird gene expressions, but it's probably nothing to worry about when it comes to breeding feeders.
As for the cannibals, the prion disease was similar to BSE - mad cow disease. It's not from breeding, or cannabalism in general, it's from eating central nervous systems that contain these nasty little prions. Basically, if you're going to eat someone, it's best to pass on the brains.
The death of chameleons unexpectadly is probably a result of inexperience the vast majority of the time. They're complex animals, and there is not purina chameleon chow made for them. The nutritional balance is purely up to the individual keeper, an dsubject to such a degree of variation, that seemingly simple things kill chameleons most of the time.
We're used to the idea that an animal that eats, drinks and sleeps well is doing just fine. You have a dog or cat that eats and drinks and sleeps - it's going to be fine most of the time without much else.
With reptiles, and chameleons in general, the variables are so great, and the knowledge of keepers so varied, that it is impossible to determine "what went wrong" for someone else, without knowing exactly what they did every day from day 1 till the death of the animal.
Plus, the anonomity of the internet allows people to not always tell the whole truth.
If someone asks why their chameleon died, they might not be saying exactly everything they did. Like the fact that the little veiled was kept with a few big males - for company, or that the animal never recieved supplementation, or lacked a basking bulb.
There's always a reason for their illness and demise, and most of the time it's "simple" only if you know everything. If you dont' know everything, the death becomes mysterious.
As someone who has kept chameleons before they "lived" (people used to say they couldn't live in captivity), I saw this behavior evolve over time.
In the 80's and 90's, most people would get sickly, parasitized, weak and mistreated animals imported to the US. These animals woudl rarely thrive. The assumption (for decades) was that the species' themselves were unsuited for captivity. They (of course) would never blame their own ignorance abou the animals needs and habitat. They didn't know the whole picture. Had these people understood the treatment the animals recieved during capture and export, and how this treatment conflicted wiht chameleons' needs and behavior, they might have understood WHY the animals were dying. They didn't know, so they just assumed (logically)that the animals couldn't live in captivity.
Of course, the early keepers were far less intuitive... they just believed that all chameleons lived less than 2 years... since that's about how long they lasted. Makes sense. Not good sense, but it is crude logic. Monty Python logic, yes, but logic.