He must have had a really big heart

I checked the wiki looks like doctor told him and he embraced it.

1938, Hitler's doctors put him on a meat-free diet, and his public image as a vegetarian was fostered; from 1942, he self-identified as a vegetarian.

Several eyewitness sources maintain Hitler was a vegetarian because of his concern for animal suffering, noting that he was often distressed by images of animal cruelty and suffering

Dude gassed people but was distressed by animal suffering is weird to me.