Cannibal Holocaust
If you've actually seen this film, you probably know why it got banned. Cannibal Holocaust is one of those "found-footage" movies that feels too graphic to be convincing, but somehow its authenticity sticks. This movie was hugely influential, but it has been equally demonized and censored.
This is the Most Banned Movie Ever, Period.
Cannibal Holocaust came out in 1980. It was immediately banned in 40 countries, but over time those countries eased their grip over the media that the world craves to consume. That being said, this horrific, gore-laden movie is still banned in New Zealand.