Re: Portman & Obama: get as angry as you want, but:
(1) if, as many have argued, it's "selfish" and "narcissitic" for Portman to switch his gay marriage view because he realized the effect discrimination will have on his gay son (and I don't disagree with that characterization), then the same must be true of others who attributed their switch on gay marriage to realizing that discrimination harms gay people close to them, as Obama did when explaining his switch (http://abcnews.go.com/Politics/transcript-robin-roberts-abc-news-interview-president-obama/story?id=16316043&singlePage=true).
(2) What Portman did is incredibly common. The primary reason there has been such a monumental opinion shift on gay marriage is because more and more gay people have come out, which made more and more people realize that those close to them were gay, which in turn made them less willing to support discriminatory laws:
It may be selfish and narcissistic to support equality only once you realize inequality harms those you care about, but that has been a very common dynamic - among people from both parties and across the ideological spectrum, whose switch from opposing gay marriage to supporting it was triggered by a very similar experience to the one motivating Portman.
That's why coming out has been such a powerful act: because people are less willing to support discrimination when they they realize it harms those they care about. It's true in general: it's much harder to demonize people when they're familiar.
I wish it weren't that way. It'd be nice, for instance, if fewer people supported US militarism and aggression and civil liberties abridgments because those who are victimized are Invisible and Distant Others, but, as Tejun Cole pointed out (http://www.motherjones.com/media/2013/03/teju-cole-interview-twitter-drones-small-fates), that "empathy gap" is a major reason why US aggression and militarism are tolerated: because it doesn't kill people whom most Americans care about.
Portman's explanation is far from aberrational or confined to one ideological group: it's how political opinions are often shaped and how political progress is often achieved. And it's definitely the leading reason why so many people who opposed gay equality a short time ago now support it.