***The bottom line: back in the 1990s, Judge Posner was somewhat open to same-sex marriage as a policy matter (to be decided by a legislature), but not as a matter of constitutional law (to be decided by a court). What led him to decide, in the 2014 case of Baskin v. Bogan, that the Constitution requires marriage equality?
By the summer of 2014, the tide was running strongly in favor of invalidating such prohibitions, although it was not certain that the Supreme Court would go with the tide. I do think the change in public opinion was decisive for all the courts that ruled in favor of creating a constitutional right to same-sex marriage. Law is not a science, and judges are not calculating machines. Federal constitutional law is the most amorphous body of American law because most of the Constitution is very old, cryptic, or vague. The notion that the twenty-first century can be ruled by documents authored in the eighteenth and mid-nineteenth centuries is nonsense.
The arguments against same-sex marriage were never strong. They didn’t need to be when there was overwhelming passionate objection to such marriage. When the objection faded (not completely, but to a great extent, and with remarkable speed), the absence of strong arguments against same-sex marriage, and the presence of strong arguments in favor of it, became the decisive factors guiding judicial action.