As if facing down violent Islamist fanatics isn’t enough, Muslim reformers now have to dodge attacks from the American left. Consider the Southern Poverty Law Center’s decision last week to brand two such reformers, Ayaan Hirsi Ali and Britain’s Maajid Nawaz, as “anti-Muslim extremists.”

Founded in 1971 by civil-rights activists, the Montgomery, Alabama-based law center says it’s committed to “fighting hate and bigotry and to seeking justice for the most vulnerable members of our society.” That apparently doesn’t include civil...