From the Wall Street Journal of all places.

Excerpt:

The two-parent family has declined rapidly in recent decades. In 1960, more than 76% of African-Americans and nearly 97% of whites were born to married couples. Today the percentage is 30% for blacks and 70% for whites. The out-of-wedlock birthrate for Hispanics surpassed 50% in 2006. This trend, coupled with high divorce rates, means that roughly 25% of American children now live in single-parent homes, twice the percentage in Europe (12%). Roughly a third of American children live apart from their fathers.

Does it matter? Yes, it does.

[…]In an essay for the Institute for Family Studies last December, called “Even for Rich Kids, Marriage Matters,” University of Virginia sociologist W. Bradford Wilcox reported that children in high-income households who experienced family breakups don’t fare as well emotionally, psychologically, educationally or, in the end, economically as their two-parent-family peers.

Abuse, behavioral problems and psychological issues of all kinds, such as developmental behavior problems or concentration issues, are less common for children of married couples than for cohabiting or single parents, according to a 2003 Centers for Disease Control study of children’s health. The causal pathways are about as clear as those from smoking to cancer.

More than 20% of children in single-parent families live in poverty long-term, compared with 2% of those raised in two-parent families, according to education-policy analyst Mitch Pearlstein’s 2011 book “From Family Collapse to America’s Decline.” The poverty rate would be 25% lower if today’s family structure resembled that of 1970, according to the 2009 report “Creating an Opportunity Society” from Brookings Institution analysts Ron Haskins and Isabel Sawhill. A 2006 article in the journal Demography by Penn State sociologist Molly Martin estimates that 41% of the economic inequality created between 1976-2000 was the result of changed family structure.

Earlier this year, a team of researchers led by Harvard economist Raj Chetty reported that communities with a high percentage of single-parent families are less likely to experience upward mobility. The researchers’ report—”Where Is the Land of Opportunity?”—received considerable media attention. Yet mainstream news outlets tended to ignore the study’s message about family structure, focusing instead on variables with far less statistical impact, such as residential segregation.

So where does single motherhood by choice come from? The libertarian Cato Institute explains:

[T]he evidence of a link between the availability of welfare and out-of-wedlock births is overwhelming. There have been 13 major studies of the relationship between the availability of welfare benefits and out-of-wedlock birth. Of these, 11 found a statistically significant correlation. Among the best of these studies is the work done by June O’Neill for the U.S. Department of Health and Human Services. Holding constant a wide range of variables, including income, education, and urban vs. suburban setting, the study found that a 50 percent increase in the value of AFDC and foodstamp payments led to a 43 percent increase in the number of out-of-wedlock births.(7) Likewise, research by Shelley Lundberg and Robert Plotnick of the University of Washington showed that an increase in welfare benefits of $200 per month per family increased the rate of out-of-wedlock births among teenagers by 150 percent.(8)

The same results can be seen from welfare systems in other countries. For example, a recent study of the impact of Canada’s social-welfare system on family structure concluded that “providing additional benefits to single parents encourages births of children to unwed women.”(9)

[…]Until teenage girls, particularly those living in relative poverty, can be made to see real consequences from pregnancy, it will be impossible to gain control over the problem of out-of- wedlock births. By disguising those consequences, welfare makes it easier for these girls to make the decisions that will lead to unwed motherhood.

So, if the Democrats opposed income inequality, they would oppose single motherhood by choice, and they would oppose the welfare that causes single motherhood by choice.

But of course the Democrats oppose none of those things, and they have worked to undermine the 1996 Welfare Reform bill while at the same time expanding the welfare payments that make single motherhood easier.