I think Eliezer believes that chickens aren’t sentient, and at the time of writing HPMOR, he probably thought this was the most common position among people in general (which was later contradicted by a poll he ran, see https://www.facebook.com/yudkowsky/posts/10152862367144228 ). If Dumbledore believed that chickens weren’t sentient, he might not think there’s anything wrong with setting fire to one.
I think Eliezer believes that chickens aren’t sentient, and at the time of writing HPMOR, he probably thought this was the most common position among people in general (which was later contradicted by a poll he ran, see https://www.facebook.com/yudkowsky/posts/10152862367144228 ). If Dumbledore believed that chickens weren’t sentient, he might not think there’s anything wrong with setting fire to one.
For lots of discussion about Eliezer’s and others’ philosophy of mind, see https://rationalconspiracy.com/2015/12/16/a-debate-on-animal-consciousness/