Okay, those are fair arguments for why it was wrong, which I don't disagree with. I just don't see any justification or explanation for what's animalistic about it. I'm assuming we're talking about the fact that they are dragging him around and slapping his head. Which guy hasn't been in a fight? If it's animalistic then we are animals. No wait...
The point is, we are all capable of this. I'm gonna throw an idea out there. We are taught not to behave like this because of the principle that you are guilty until proven innocent, so that an innocent person does not receive unfair treatment for something they didn't do. Gaddafi killed many thousands in the massacres that led to the civil war. We can't know that he did it, we can be very sure though. He refused to listen to the majority of his people and instead went to war with them. Let's assume the people in this video lost family members, friends, and so forth in the attacks. In that context I don't see animalistic behavior, I see expected human behavior. The fact that he was killed was judicially and ethically wrong. I just don't like the word "animalistic" I guess.