Shouldn't animals be the ones insulted to be compared to humans?

I just finished watching Braveheart and finished reading the actual details of the real Sir William. He was disemboweled. I read more on how it was done and I was totally grossed out. I know in war there are very many things that are done that are inhumane but it got me thinking how people hate to be compared to animals. Last I checked animals don’t torture their prey. Ok, a cat may toy with his but at least he eats it to survive. We don’t just kill to survive. Humans have a long history of being something way worse than any animal.
So why do some get offended at being compared to an animal?