Joan Blades describes herself as, among other things, a “nature lover” and a “mother.” She is also a co-founder of the liberal activist group MoveOn.org and a regular contributor to the liberal blog The Huffington Post. In a recent post, Blades wrote about an article she read in her local paper. It described a group that supports the kind of measures Blades expected liberals like Huffington Post readers to support: health care for children, “fair wages,” and flexible work schedules for moms. What Blades found surprising were some of the comments that came into the paper’s website. One person “reasoned”...