But believers in the Bible really do reject the Koran, and believers in the Koran reject (the extant versions of) the Bible (which they claim are corrupted, as can be "proved" by noticing that they disagree with the Koran). Whereas in the vegetarianism examples, there is no mutual rejection, just people who emphasise a particular point while also accepting others. Many of the people who go veggie to prevent animal suffering would also agree that it causes environmental damage. It's just that their own emotional hierarchy places animal suffering above environmental damage, not a real disagreement about the state of the world (same map of the territory, different preferred locations).