Homer clumsily attempts to build Marge a spice rack. While he is doing so, Maggie sneaks up behind Homer and hits him on the head with a mallet, similar to the famed stabbing scene in the movie Psycho. Marge is initially clueless as to what would motivate Maggie to do such a deed, but then notices that, when Maggie sees an episode of The Itchy & Scratchy Show, a cartoon which is known for its violence, she mimics its content. As a result, Marge immediately blames the makers of the show for Maggie's actions and bans Bart and Lisa from watching the show, but the two still manage to watch Itchy & Scratchy at their friends' houses. Marge writes a letter to the producers of the show asking them to tone down their violence, but in response, Roger Meyers, Jr.—the chairman of Itchy & Scratchy International—writes a letter to Marge, telling her one-person can not make a difference and calls her a "screwball". In response, Marge decides to "show what one screwball can do".
Marge forms "Springfieldians for Nonviolence, Understanding, and Helping" (SNUH as acronym), and forces the family to picket outside the Itchy & Scratchy Studios. Marge's protest gains momentum and soon more people join the group and even start to picket The Krusty the Klown Show, on which Itchy & Scratchy is shown. Marge appears on Kent Brockman's show, Smartline where she confronts Roger Meyers over the violence and suggests that concerned parents send letters to Meyers. Many angry letters are sent to the Studio and Roger Meyers concedes defeat, and agrees to eliminate violence in Itchy & Scratchy. Eventually, a new short in which Itchy & Scratchy sit on a porch drinking lemonade airs, but Bart, Lisa, and other kids across Springfield reject the cleaned-up show. A lengthy montage follows, in which the children of Springfield go outside and engage in various wholesome activities and that night Bart and Lisa brag about their various outdoor activities while Marge listens happily.
Meanwhile, Michelangelo's David goes on a coast-to-coast tour of the United States, and Springfield is one of its scheduled destinations. The members of SNUH try to urge Marge to protest the sculpture, insisting that it is offensive and unsuitable. However, Marge, being an artist herself, reveals that she believes that the sculpture is a masterpiece. While appearing on Smartline, Marge admits that it is wrong to censor one form of art but not another, and sadly concludes that while one person can make a difference, at the end of the day they probably should not. Freed from public protest, Itchy & Scratchy immediately returns to its old form and Springfield's children abandon their wholesome activities and return to spending every day indoors watching the violent Itchy & Scratchy cartoons. Homer and Marge go to see David and Marge expresses her disappointment that the kids are at home watching "a cat and mouse disembowel each other" rather than seeing the sculpture. She cheers up when Homer tells her that the school will be forcing them to see the sculpture on a school trip.