Audio problem: In Maroon's office, when he says to Valiant "I want you to get me a couple of pictures to wise up the Rabbit with," notice the next shot is of Maroon from the back of his head. Notice his mouth doesn't match the words he is saying. (00:06:30)
Visible crew/equipment: When Eddie is bouncing up and down on the pogo stick at the Acme Factory, two wires are visible around his left and right shoulders; just before he bounces up into the light fixture.
Continuity mistake: After Roger springs onscreen from an underground pipeline at the Acme Factory, a steel grate is thrust high into the air, falling right in front of Judge Doom (however the shot cuts away half a second before it's supposed to hit the floor). But two shots later that same grate is seen falling from a much higher elevation again. It should have been lying on the floor at this point. (01:21:10)
Continuity mistake: When Roger starts reading Marvin Acme's will out loud, Jessica takes her left hand and rubs his head, but once the shot changes her hand is nowhere to be seen. (01:35:05)
Continuity mistake: When Benny the Cab approaches a bridge where the woman is pushing her baby carriage, the sun casts shadows at wildly different angles in alternating shots. (00:59:30)
Continuity mistake: After Greasy starts up the dip machine, the number of ropes tied around Jessica's midsection changes from two to three within a couple of shots. (01:22:30)
Revealing mistake: After Bongo the Gorilla Bouncer tosses Eddie into a pile of garbage cans in the back alley, Eddie lifts himself up and here we can see that he's wearing knee pads beneath his pants. (00:21:25)
Revealing mistake: After Roger reads Marvin Acme's will out loud, all of the toons start jumping for joy. Meanwhile the music machine is still activated in the background, and its colorful flashing lights are being reflected on the ground near Betty Boop and Tweety at the front of the crowd. With all of the toons grouped together like they are, the machine's colorful lights should have been obscured, not reflected. (01:35:30)
Revealing mistake: During the Toon Patrol chase, before the cab enters the alleyway there's a wide shot of the cab making a fast turn. Valiant has his head down, with his hat covering his face and his body totally motionless, opposite to what he looks like in the close-ups where he is grabbing the steering wheel, his head up and controlling the car, thus revealing that the actor was replaced by a dummy in some of the shots. (00:58:40)
Continuity mistake: At the end of the movie, when the spray-machine breaks the brick wall with the word 'Keep Clear' painted on it, the first 'E' and the 'A' get destroyed, but appear rebuilt a second later.
Continuity mistake: When Doom writes on the bar's blackboard "Rabbit Dip" the look of the text keeps changing all the time: sometimes it's neat, others it's fuzzy, and others some letters are missing. (00:52:10 - 00:53:10)
Continuity mistake: When Eddie hitches a ride on the back of the Streetcar, only its rear power-arm is attached to the overhead cable. Later when Eddie jumps off and says "Thanks for the cigarettes", it has both of its power-arms raised. (00:10:10)
Continuity mistake: In the scene after Valiant gets rejected by the trolley operator, notice as the trolley operator is closing the door, Valiant starts to fold the check. But in the next shot, he starts folding it again the same way. (00:09:35)
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)
Continuity mistake: In the scene where Hoskins is washing his clothes and hiding Roger notice that the weasel talking is holding a gun. Hoskins puts a bar of soap in his mouth and the gun disappears. Then when he comes back to Hoskins the gun reappears. (00:42:15)
Continuity mistake: In the scene where the weasels are in Eddie's office, when the other four weasels see their leader falling down the stairs, Stupid (the fat weasel) closes the middle drawer on the filing cabinet. In the next shot the drawer is open. (00:42:20)
Continuity mistake: In the scene where the gorilla is throwing Hoskins out of the club notice he is facing forward but when he lands in the trash he lands on his back. (00:21:20)
Continuity mistake: At Valiant' office notice the bottle of whiskey on the table, right before he examines the pictures of Jessica and Acme, the bottle is about almost full. But in the next scene after he finds out that Roger is there he sits down and you hear him pour himself a drink. In the next shot the bottle is almost empty and he is holding a glass that only holds about a mouthful of whiskey. How could he pour that little amount of whiskey and lose that much? (00:36:00)
Continuity mistake: In the scene at Valiant' office, Roger starts reading the letter but when he jumps off the bed in front of Valiant, the letter disappears. (00:38:35)
Continuity mistake: Mr. Maroon talks Valiant into working for him, he has his head tilted sideways. A brief back shot shows the head straight, but the immediate front angle shows it tilted again. (00:06:55)
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.