Whether we are nice to animals or not, or whether they are nice to us or not, is irrelevant.
What matters is how animals treat each other.
...
Chickens do not ... treat each other ... well.
.
For that matter, most animals don’t. The best they can do is treat their own kind well. To them, that which is not their kind is either prey, predator, or something to be ignored or avoided.
Some animals rise to the level of social animals, but few can be said to have any kind of ethics, or measures of behavior that could be considered “sinful”, or “not sinful”.
There are behaviors that promote survival, and behaviors that reduce it. There is no good beyond survival, and no bad beyond being wasteful of resources.