I'm not making any assumptions - I simply took the man at his word, based on his statements.
I don't disagree with your sentiments - it's a major reason why I'm no longer a practicing Catholic. However, it is still my view that, as Senator Portman stated himself, he changed his position on gay marriage after his son disclosed he is gay. As such, that makes him, in my view, unfit to be President or Vice-President. A person in the highest leadership positions does not make decisions affecting hundreds of millions of people based on the dynamic of his or her family life. I'm sure his son isn't the first person who told Portman he was gay and expressed a desire for equality in marriage. Is Portman's son "special" in a public policy sense or just special because he's Portman's son? Does Portman's son have other "special" public policy positions that dad will acquire based on his relationship?
I suppose, to follow your logic, if Portman was President and a relative of his, perhaps his son, was kidnapped by terrorists, it would be okay to change the US position on negotiating with terrorists and maybe release all Islamic prisoners. After all, he's just "reevaluating" his "view/thought/actions/ideas" based on his personal experiences.
Perhaps to you it may sound callous - if so, you're not fit to be President either - when you run for the highest public office, personal family dynamics do not rule public policy.