It must have seemed the perfect time for a social media-meets-political-protest moment. Earlier this month, New York City Mayor Mike Bloomberg said, "You have a lot of kids graduating college who can't find jobs. That's what happened in Cairo. That's what happened in Madrid. You don't want those kinds of riots here."

Some do. Editors at Adbusters, a Vancouver-based magazine (mission: "topple existing power structures") wanted to see if they could spark demonstrations just by posting the idea using...