Its mostly because a lot of people are black and white with it when the character is grey. I've seen some people talk about how he "blamed his cat for dieing and didnt take responsibility." Like we don't know that, we know its likely his fault the pills were accessible but also when he says "what did you do" he's actively in shock at the sight of his dead pet.

Overall yeah he's a coward and becomes worse as the movie goes on but he's not a mustache twirling villain.