I'm in fundamental agreement with Garfield on this one. I can understand Jon's resentment that the cat doesn't appreciate the meals Jon prepares, but his way of expressing this is probably not the most logical.
I particularly like Garfield's way of refuting this by also angrily demanding more food, which denies acceptance of what Jon is really saying: "You know you shouldn't eat so much, here is a possible means of preventing overeating." Second party willfully misunderstanding first party that they may continue self-destructive behavior? Always a great joke.