They shouldn’t have died like this. We shouldn’t have to live like this.

When most of us think of April, we associate it with spring. But for researchers who study extremism and violence, the month has other, darker connotations: “We sometimes refer to April as the beginning of the killing season,” one told the Washington Post in 2016.

This year appears no different. Four people were killed and 28 injured this weekend when a shooter opened fire at a Sweet 16 birthday party in Dadeville, Alabama. According to the Gun Violence Archive, there have been more mass shootings than days so far this year: The Dadeville...