John Waters said that after filming the chicken death scene in Pink Flamingos; they cooked, and ate the bird. Plus, the chicken became a movie star...which is a whole lot better than what happens to most chickens.
I'd assume that the same went for the chickens killed in Mondo Trasho. If the chickens go to good use, and end up living eternally through the magic of the cinema, I can't really say that I object Waters' opinion on the subject.
As far as Cannibal holocaust is concerned:
Cannibal Holocaust is overrated. However, the controversy STILL surrounding the film really goes to show that the film really did succeed in shocking it's audience. The highlights (few and far between) of the film are absolutely horrific, despite a majority of the brutality being staged.
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Cannibal Holocaust is not merely focused on the societal taboo of flesh eating. The greater theme of the film is the difference between the civilized and the uncivilized. Though the graphic violence can be hard for most to stomach, the most disturbing aspect of the film is what Deodato is saying about modern society. The film asks the questions 'What is it to be 'civilized'?' and 'Is it a good thing?'"
- Carter, David.
"Savage Cinema". Savage Cinema.
http://www.savagecinema.com/cannibalholocaust.html.