I don't know that gay marriage is the sole example of the court being ahead of the people that you can point to in history. Brown vs. Board of Education came 10 years before the Voter Rights Act. It's not always possible to know how long one of the other branches would have taken to move the country forward. I think it's more fair to say that each branch has its moments of lurching ahead and falling behind. More importantly, each is entirely made up of people, and you may find that the lurches and dragging are directly related to the people. If we want to see the Supreme Court drag us backward for the next 50 years, then we can certainly just tell everyone that they should never have trusted the Supreme Court to begin with and certainly shouldn't now. I don't think it's that simple, and it certainly doesn't have to be that way.
Regardless, Kavanaugh's confirmation is less about dragging, since an equally qualified justice would have dragged the court behind for decades to come - it is about integrity, since Kavanaugh is a proven liar and a proven violent offender who has evaded justice at many turns and seems to know nothing about what it stands for.