Other mistake: At the beginning of the movie, when Roger is begging the director to give him another chance and keeps grabbing the bottom of the director's jacket that is in the director's hand, at one point the bottom of the jacket leaps into Roger's hand before he actually grabs it. (00:05:05)
Other mistake: When Eddie Valiant gets thrown out of the Ink and Paint Club, he is already starting to go through the air as the gorilla moves his hands to throw him. (00:21:20)
Other mistake: Three shots after Eddie stuffs the soap into Smart Guy's mouth, when the other four weasels notice him tumbling down the stairs, a chair can be seen flying across the room. This is impossible, because the other four weasels are together, and Smart Guy was talking with Eddie, so there was nobody to throw the chair. (00:42:15)
Answer: There's really a lot of possible reasons he hates other toons. There's a whole Roger Rabbit book and comic book series that explain Doom's background more. In the film, he's greedy and wants to destroy Toon Town to build the freeway to make more money. In human disguise he's also seen as merciless and is just punishing toons to maintain law and order, etc. Although that's just an excuse to kill toons as well. However, not explained in the film; as a toon he was cast as the antagonist in cartoon films until an accident one day left him thinking he was an actual villain (as opposed to just an actor playing one). That's when he began his life of crime, including killing Teddy Valiant. So his hatred of toons is more about him being evil and not a personal vendetta against them, like Blade's motives.