Social scientists have been tracking the outcomes of children in various family formats for the past century, many in long-term studies of 30 years -- I'm thinking of the work of Judith Wallerstein here, among other reputable researchers. They have found that while individual persons may do well coming from many kinds of upbringing, the most successful group of people in terms of school performance, getting a job, staying out of trouble, having good health and having good relationships themselves with a spouse and children, statistically are those raised by both biological parents, married and living together.
Such studies reinforce what the author is trying to get across: family form matters. Deviating from the known best situation has consequences and can affect many individuals negatively.