John Evans is in no hurry to get married. The 25-year-old returned LDS missionary lives with his parents, works full time, takes night classes toward an English degree and, with law school looming, is building up his savings. Evans goes on dates, but they tend to be expensive so he prefers developing friendships first. Sometimes he finds it easier just to hang out with the guys at his Mormon fraternity. “My dating pace is right for me,” Evans says. “I don’t feel stressed.” That kind of modern nonchalance is what may be worrying LDS President Thomas S. Monson and other...