In the days since officials detained suspect Tyler Robinson for allegedly assassinating political influencer Charlie Kirk, polarizing discourse has appeared online as political groups try to pin the tragedy on each other: “The Left is the party of murder,” Elon Musk posted. “I can’t name, including probably like Al-Qaeda and the Taliban, a group that is more violent per capita than the radical trans movement,” Donald Trump Jr. said on The Megyn Kelly Show on September 11. On the...