Anonymous Reader suggested in the discussion of the last post that welfare law changes in the 1960s might have also played a role in encouraging illegitimacy:

Dalrock, it seems to me the most likely direct influence on illegitimate children would be the Great Society. I have been told by people who were around as adults in the mid 1960′s that before the LBJ political landslide, Aid to Families with Dependent Children (AFDC) was available only to women who had been married. Widowed or abandoned or divorced, made no difference, but the claim made is that it was not available to women who had bastard children until after LBJ I cannot confirm this, so far am unable to determine the requirements for such aide prior to 1964-65. … So the question that ought to be investigated is this: did the rules for AFDC, public housing, and other mother-and-child protective aid change in the mid 1960′s?

With just a bit of google searching I found The Legal History of Aid to Dependent Children Program which corroborates what he had been told.

A provision in the law that authorized ADC assistance only to “suitable homes” functioned, in the program’s first three decades, to reduce the number of eligible children (in 1960 when 79 of every 1000 children were in need, only 30 received assistance) and, particularly, to inhibit coverage of “illegitimate” children and children of color. Local ADC policy frequently discontinued coverage during seasons when low-wage labor was short in fields or homes, thus forcing poor mothers into such labor. For its first three decades, AFDC operated much like a private charity, with its case workers given discretion in investigating clients, cutting off benefits to those determined to be unsuitable, and reducing benefits to those found in violation of any of AFDC’s myriad regulations.

Radical agitators fought to establish welfare as a right:

The overarching objective entailed establishing a federal constitutional right to a minimum adequate income.

According to the paper, they were largely successful in this through a series of court rulings.

See also: The blurry line between the welfare state and child support