Last week, Sen. Rob Portman (R-Ohio) made news by announcing that, upon learning his son is gay, he has changed his position on gay marriage and now supports it.

It wasn’t unpredictable that there would be those on the political right who would criticize him for his change of heart. But what disturbs me is the blowback he is getting from some on the left.

I’ve seen a lot of social media chatter, since Portman’s announcement, along these lines: “So it took his son coming out for Portman to change his tune—why didn’t anybody else’s sons or daughters matter to him?”

First of all: Really? A Republican changes his mind and takes your side, publicly, on a crucial civil rights issue, and the first thing you do is criticize him for his motives, or for not doing it soon enough? Focus, people, will you?

Why Senator Portman changed his mind doesn’t really matter. The fact is that, regardless of his motives, he has taken a courageous stand that is almost certain to create political problems for him with at least a segment of his base. Any time a conservative changes his or her mind on this issue, that’s another crack in the wall of intolerance.

But there’s another reason why this is important. Remember when President Obama said one of the key characteristics he was looking for in a Supreme Court justice was empathy? Republicans reacted as if he had committed blasphemy.

Senator Portman’s love for his son enabled him to have empathy, and when that light of empathy went on over his head, he was able to extend it to everyone in the LGBT community and publicly change his position on marriage equality. That’s huge, and it took real guts. But more than anything else, it demonstrated the power of empathy in promoting progressive change.

The reason why the enemies of change are so afraid of empathy is pretty simple. It’s much harder to support policies that hurt a particular group—gays, the poor, ethnic minorities, etc.—when empathy enables you, for a moment, to walk in their shoes and see them as fellow human beings. Senator Portman has demonstrated—intentionally or not—why empathy is the number-one weapon against the opponents of social progress.

The Republican Senator from Ohio should be congratulated and praised for his decision, and those of us on the left should do a better job of understanding what it means: When people feel empathy, we win.