A line of legislative deference has been "legislatures get to define 'marriage' because the Constitution is silent on it". This is true, they can define the constellation of benefits and requirements generally. But the Constitution isn't silent on the extent of franchises: they have to apply equally. You can't craft special privileges for one group and not another without "due process of law". As the judicial consensus has evolved on this, we've seen the introduction of "rational basis plus" to deal with gay marriage, where the old rational basis standard is married to the proviso "except when animus is involved". That is, the legislature may define a variety of differences arbitrarily, but they can't do so out of animus. That would require higher levels of justification, more "due" in due process.
This has been the challenge 150 years now, since the creation of the 14th Amendment permanently dissolved any pretense that State or Federal governments were inheritors of royal powers. They can't actually just make laws arbitrarily, they have to put some force of public reason behind discrimination at least equivalent to how fundamental the right is. Working out to what extent we actually have a government of limited powers versus king-and-parliament in republican garb has been a long process. It is no secret and, I suspect, no shock that you will find conservative jurists involved in a queer Anglophilia. While they may discuss a government of limited powers, in practice they mean a government balanced against rights inhering in an elect. Just as the old law of England, in its manifest cruelty and inequity, proclaimed differences among its subjects even into their graves.
The startling disingenuousness of conservatives is rarely apparent to them because, generally, conservatives speak from that position of largely unacknowledged priority, those whose rights are immediately protected rather than prorogued. The hypothetical state which outlawed opposite- but allowed same-sex marriages would be condemned by conservatives as violating a fundamental understanding of marriage to which they have a right. But that state is always hypothetical, they can deny their probable response because they will never have to give it. One thinks of what Scalia, et al, would declare regarding the Panther's law in a free state of Oakland. Perhaps they would find, suddenly, that protections of minorities are fundamentally consistent with their views. That these are ever hypothetical examples, that no conservative lives under such a pall as they cast on others, is critical to their blindness. It is how they can declare some right both fundamental to man and unequally applied. Their world is not the one turned upside down, their dignities not those trampled. They require of others that their homes be built of crooked wood, keeping what little straight lumber man produces for themselves alone.
So we get here. It was conservatives who asserted that marriage is a fundamental, bedrock institution, one of these few sources of straight timber in a crooked world. But they have also been quick to assert that it is reserved to their favored. We have seen this over and over, the majority in Obergefell lists some in marriage expressly, like the removal of coverture and miscegenation laws. That's not what the Republic established in 1868. It proclaimed equality before the law, we partake in the straight and crooked together or not at all.
The 14th Amendment holds, merely, that if you find a fundamental right among one group, it's a fundamental right for all groups. You don't get a special group with rights and another without. Ultimately, there was no way for conservatives to win: the pure logic of the situation means that every argument they give in defense of not having same-sex marriage stresses ever greater the fundamentality of a marriage right. That tension cannot hold forever because it creates a deep perversity in the law, a strange exception which people accept less and less.
We know this because we lived through that process. What held together conservative arguments in public was disgust for gays, real hatred. As it waned, there was less reinforcement available and all the same tension in place. As the rapid expansion of gay marriage showed, it was unsustainable.
Conservative pundits have been quick to say "the democratic process has been cut short". It hasn't. Even cursory examination of the rhetoric and reason bearing in gay marriage legalization shows that people saw themselves as doing what the courts should have but had so far failed to do. This wasn't a democratic process in the normal sense, it was the people fighting a court which had fallen behind. For the court to, once more, recognize that the 14th Amendment means what it damn well says -- by force of statute if not by reason alone -- is all this "democratic process" was intended to do. Had this been accomplished by court packing, no one would have seen it as a lesser achievement.
Thus we get where we are today, with an argument opened up for five justices who wanted to grant gay marriages. It's worth bearing mind that the bans were in large measure electoral ploys. Roughly half were enacted in 2004 as part of a strategy to increase evangelical turnout. The other half were backed in 2008 for precisely the same reason. When we speak of the democratic process, we are usually speaking of a free deliberative system that the bans do not, in large measure, result from. They're bits of electoral strategy and, once known, seem a perversion of democratic politics. Perhaps even another in a long list of destructive referenda. Given the underlying weakness, it's hard to have expected them to survive without procedural hurdles to save them. And that reduction, the loss of core democratic legitimacy and their mere procedural preservation, makes this 5-4 ruling as solid as if it were 9-0.