The family that Santorum refers to is what he calls the "natural family"; mom, dad and the kids. Other potentially viable variations on this arrangement (single-parent, gay couples) are incompatible with a successful society.
The Senator's opposition to families led by gay couples is unsurprising. Santorum famously stated that gay marriage would eventually lead to human-animal partnerships listed in the New York Times' wedding listings. However, his opposition to families led by single mom's is surprising. His criticism is that children need a father's influence and the large numbers of fatherless families have a negative influence on society. It's a criticism that neglects the fact that not all single-parent families are that way by choice.
Schmitt's review of the book hits on a theme that has become more and more obvious as more people stop to look at the ideas conservatives are trying to sell people on. It's an extension of the liberal ideas encapsulated in the trappings of conservative tough-mindedness.
It doesn't always translate, as Schmitt points out. In order to disguise the fact that many Republican politicians are conceding the inherent popularity of liberal economic programs, they must go a little further in reinforcing their conservative credentials to prove they are not also buying into liberal social ideas. What Schmitt calls,
"a mean-spirited, intolerant liberalism."
As Rick Perstein pointed out in a recent speech, the Republicans are deathly afraid that Democrats will return to their economic populist roots. Perlstein quoted Bill Kristol:
Health care is not, in fact, just another Democratic initiative . . . the plan should not be amended; it should be erased. . . . It will revive the reputation of the . . . Democrats, as the generous protector of middle-class interests.
As some Democrats move towards the Republicans on social issues, they miss the fact that the Republicans are moving in their direction on economic issues and while using social issues as cover. Santorum is just one example.