100% bingo -- the freely available option has created a holocaust where once there was only a trickle. But I would add, legal abortion/birth control also eliminated accountability for men -- it's all the woman's problem. If she gets pregnant, cads urge abortion or shirk child support and must be sued. Rarely does casual sex result in a marriage or a stable home for a child.
It was a long, slippery slope from the early 60s, when the SCOTUS affirmed in Griswold v. Connecticut that the family is the basic unit of society, to where we are today. The Court's very next reproduction-related decision was to extend the right to distribute birth control to the unmarried as well as married people wishing to control the size of their family. That decision greased the skids for Roe, which would immediately follow. Those two SCOTUS decisions, plus the California Lee Marvin/Michelle Triola "palimony" case in 1977 were the end of marriage as a social institution. From then on, it has been, as far as our SCOTUS jurisprudence is concerned, an outmoded folk tradition.
Excellent post!