Sorry. But I dont really buy that this is racist.
Marcie is sitting by herself, so is Linus. The only reason that Charlie/Patty/Snoppy are sitting squished together is for the staging requirements of the scene. (Patty's "who cooked this?!", Snoopy sinking, then her berating Charlie Brown, and he leaves). They both had to be next to eachother for the joke/berating to land.
The rest is due to the askew Peanuts brand perspective, and if you look closely *everyone's* chair is different. The reason they likely gave Franklin the lawn chair was to at least get ONE gag out of him. Franklin historically has some of the least personality traits of all the peanuts gang next to maybe Shermy. Everyone at the dinner gets a moment, Franklin sinking into the chair is literally the only time they cut to him in the dinner.
That said, this is one of the worst Peanuts specials for other reasons.
Yeah, people are going way overboard with this. It's silly.