RebYidd23,
How is walking around on four legs and eating grass evil? Stupid if you’re human, but not evil.
Suppose you lock up an animal in a cramped space, keeping it from roaming and devoid of companionship, and you feed it inadequate food until it dies. Is that not an evil thing to do?
By acting like an animal, a human being confines his neshama, keeping it from rising, deprives it of companionship with Hashem, and fails to keep it fed via spiritual growth. Is that not an evil thing to do?