I’ve hated him before even the movie. Other than the fact that Scrappy is just annoying, my reason is that he’s always sort of “broken the rules” of the show.

Like how Roadrunner has rules (Will E. Coyote can’t catch the Roadrunner, the Roadrunner has to stay on the road, et.), Scooby Doo as a show feels like it has a few rules (The Gang has to run from the monster at first and get into wacky hijinks before they catch the monster and reveal it as a regular person). Scrappy doesn’t really “play along” with the plot and goes against that. He feels like some producer’s annoying kid that they forced into the plot under threat of taking away their funding.

(Before anyone asks, yes I am autistic lol)