Being on the "Right Side of History"

I'd like to take a brief moment to comment on a growing trend in journalism specifically in relation to the gay marriage debate. A common recurring statement in articles about this subject is that the Supreme Court will hopefully come out on "the right side of history." What does that mean exactly?

Does it mean, as I would use the expression, that the chain of effects produced by their decisions or actions will result in what is objectively true, good and beautiful? Or does it mean, as I suspect most people are using the expression in current discourse, that public opinion is shifting a certain way and that people must move in that direction in order for history books to remember them fondly in a generation or two?

If the expression "being on the right side of history" means the former, then there are ample parallels and testimonies from the past that can be used as examples for the current situation to determine whether legalizing gay marriage will be good for society. However, that takes a lot of work, thought, and effort, and we Americans much prefer an opinion poll, which is softer, fuzzier, and easier to obtain.

If the expression means the latter, then we can forgo all that hard work move straight to the opinion poll, and say that because public opinion is trending in favor of gay marriage (58% according to a recent Washington Post survey) that therefore the cause of gay marriage is "the right side of history". A word of caution though, while we're on the subject. There have been any number of times in history when public opinion, even a vast majority of public opinion, has shifted in objectively bad directions. Unlike Rousseau, I do not share the rosy view that the will of the people will always be identical to what is best for a nation. Remember where that sort of thinking got the French Revolution? I could easily imagine any number of scenarios in which the vast majority of people in a society are wrong about a particular idea. In these scenarios a poll would not show that the nation is going to end up on the wrong side of history. You can't prove something to be true or good based on popular opinion. Only objective standards and historical precedents would show that.

Here's the tl;dr:
Yes, Viriginia, ad populum is still a logical fallacy.