It’s delightful that Rob Portman now supports same-sex marriage. I don’t know how many conservatives or Republicans follow the lead of Ohio’s junior senator, but it’s a long march to equality, and every step helps. So good for him. But even so, I couldn’t help wondering: what if his son weren’t gay? Were that the case, we have no reason whatsoever to believe Portman would have taken this step. And this brings us to a difference, for my money the single most important difference, between liberals and conservatives: in general, conservatives have no social empathy. It shouldn’t take filial love and loyalty to bring a person to a position that he should reach via a simple combination of compassion and principle.

What makes a person a liberal? Lots of things, but fundamentally, it’s the ability to think beyond self-interest—to examine an issue through other people’s eyes, and to imagine such a thing as the common interest or common good. The obvious example from American history is civil rights. For your average Northern white person in 1963, it wasn’t so difficult to identify with the interests of the Southern black person. Millions of white Americans were thus “liberals” at that point in time, at least with regard to that issue. Whites were able to see the issue through black eyes, in a sense; most even saw that their own self-interest as Americans was bound up in Southern blacks’ self-interest. That meeting place of self-interest and another’s interest is exactly where the common good lives.

That was an easy case, in a way, because Northern whites didn’t have to give anything up to embrace the enfranchisement of Southern blacks. There are harder cases, cases involving questions of taxation and spending, where liberals still think beyond self-interest. This is how I’d define social empathy—the ability to put the interests of those less fortunate ahead of your own. Conservative readers are rolling their eyes, but millions of Americans take this position and live their lives in this fashion. Anyone who makes, say, a six-figure income but votes Democratic is on some level voting against her own self-interest, at least in economic terms. The Republicans are the party that is far, far more likely to look after your interests if you make $100,000 or more (although history shows also that Republicans tend to be the ones who create financial crashes and meltdowns and Democrats tend to be the ones who fix them, but that’s a different column). And yet, many millions of such Americans vote Democratic. They are willing to sacrifice some self-interest for the sake of others’ interests and of what they perceive to be the common interest.

Social empathy comes naturally to a small percentage of human beings (personally I think we’re almost all born that way, but most people, alas, start learning selfishness from an early age). Others have to learn and think their way there. And most people never bother. This is why there are fewer liberals than conservatives and always will be.

Now let’s return to the issue of homosexuality. It is true that all of us who are straight but support gay rights had to learn things, had to overcome certain negative instincts. For straight men, these instincts are visceral. Let’s be blunt about it, shall we? It’s the image of two men fucking. Many straight men can just somehow never get around that.

But—they can. That is, they could. And they should. If they had any social empathy, they would. They would try to see the world from the other’s point of view. Now, for all of us, to one degree or another, seeing this question through the other’s eyes depends on personal experience. In my case, in my mid-20s, I went from knowing no openly gay people (this was the 1980s) to having several close gay friends. That changed me, but that wasn’t the only thing that changed me. I read about it and thought long and hard about it. I decided I should change.

That was one point in history, when so much activism was really just starting. The current moment is a very different point in history. To live in this America—with so many openly gay men and women making so many important contributions to society, with so many examples among both celebrities and friends and neighbors of gay couples who demonstrate that their love is no different from straights’—and to oppose same-sex marriage is a position that is increasingly impossible to defend. And it is increasingly the case that a thinking person should just be able to figure this out. It sure as hell shouldn’t take a gay son or daughter. That’s much more self-interest than social empathy.

I suppose I should throw in a paragraph here about Obama. Yes, he was morally wrong here too, until recently. But at least he didn’t have to wait for one of his daughters to come out (not predicting anything, just playing with a hypothetical) and pour her heart out to him. And he did take his position in the heat of an election year, which took some stones. Portman chose a nice safe time, three years away from his next dance with the electorate.

So I give Portman one-and-a-half cheers. Certainly no more than that. And to the bigot Marco Rubio and the bigots who cheered him Thursday, well, I need say nothing. I’m happy to let them be judged by history—and by the voters, a solid majority of whom now feel the social empathy that America’s right wing works so long and hard every day to suffocate.