In the book
Ron didn't know Scabbers was an animagus. He only thought Crookshanks was trying to eat Scabbers. Ron literally had proof that Crookshanks possibly ate Scabbers and Hermione kept defending Crookshanks. Also Hermione wasn't completely empathetic to Ron. How would you feel if your friend's pet tried to kill your pet and your friend justified it by saying "that's what rats do" instead of being more empathetic? I'd feel pretty angry too. Also Ron had no reason to think Crookshanks didn't eat Scabbers. I'd also be pretty pissed if my friend's pet killed my pet and my friend defended their pet. Also Hermione wasn't completely responsable either. Ron's feelings were totally valid. I would've taken Ron's side too if I was in Harry's shoes or if I was a character and friends with them