I think their point is if you are a reader of Paul's work and the surrounding text you can deduce pretty soundly he isn't saying take turns in mutual abuse, but something else. Big picture, Christianity has a central, and odd tension, of sacredness of individual, but also perfect unity in community. The Trinity as the prime example. But marriage also as two flesh becoming one. Much of Christian writing is how to resolve that seeming contradiction (individuality with perfect unity and love)