"Legality didn't come into it - the law simply reflected general public opinion."
But the change in the law has led as well as reflected changing public opinion. It is easy to dismiss something if is illegal - no need to think hard about it, you (they) can't do that. Once it is legal then you CAN do it without danger from the law (but must decide how open to be), and as it becomes more open it becomes more normal in the mind of people who are happy in conventional roles themselves.