Last week, Iyad El-Baghdadi, a human rights activist born in the United Arab Emirates, tweeted out portions of a call-to-action to Muslims worldwide by Abu Bakr al-Baghdadi, leader of the Islamic State. He asked people to "rise up" and join the extremist group in their fight. Muslims on Twitter found the request hilarious, and took the opportunity to have a little fun. In an American political sphere that occasionally posits Muslims — not some Muslims, not a very, very small number of extremists — as uniform threats to national security, Twitter's collective response to Abu Bakr al-Baghdadi's request speaks to...