You are correct to question it. There are a number of things that humans would succumb to that maggots are unaffected by.

A good illustration is a duck kill that I worked a number of years ago. Avian botulism combined with oppressive heat and drought had concentrated the water holes on streams in an urban area. Ducks would die, bacT and insects set upon them and make quick work of them. However, maggots accumulated the botulinum toxin and were the source of further duck poisonings. All-told...over two locations we removed an incinerated roughly 600+ carcasses (not all ducks and some small mammals were also affected after gorging on the little insect diners). Followups were required for months and dead and dying were removed. Finally the cycle was broken but approximately 80-90% of the population of ducks and wading birds were killed.

Anyway, that's a long-winded example of why not to necessarily trust other organisms to make a food source safe for humans. Animals can tolerate things we can't, and vise versa.