"I had hesitated on gay marriage in part because I thought that civil unions would be sufficient. I was sensitive to the fact that for a lot of people, the word marriage was something that invokes very powerful traditions and religious beliefs. I have to tell you that over the course of several years as I have talked to friends and family and neighbors when I think about members of my own staff who are in incredibly committed monogamous relationships, same-sex relationships, who are raising kids together, when I think about those soldiers or airmen or marines or sailors who are out there fighting on my behalf and yet feel constrained, even now that Don’t Ask Don’t Tell is gone, because they are not able to commit themselves in a marriage, at a certain point I’ve just concluded that for me personally it is important for me to go ahead and affirm that I think same sex couples should be able to get married."
On how Michelle feels on the Issue;
"This is something that, you know, we’ve talked about over the years and she feels the same way that I do. And that is that, in the end the values that I care most deeply about and she cares most deeply about is how we treat other people. We are both practicing Christians and obviously this position may be considered to put us at odds with the views of others but, when we think about our faith, the thing at root that we think about is, not only Christ sacrificing himself on our behalf, but it’s also the Golden Rule; treat others the way you would want to be treated. And I think that’s what we try to impart to our kids and that’s what motivates me as president and I figure the most consistent I can be in being true to those precepts, the better I’ll be as a dad and a husband and, hopefully, the better I’ll be as president."
On how he came to the decision to take a stand;
"It's interesting, some of this is also generational," the president continued. "You know when I go to college campuses, sometimes I talk to college Republicans who think that I have terrible policies on the economy, on foreign policy, but are very clear that when it comes to same-sex equality or, you know, sexual orientation, that they believe in equality. They are much more comfortable with it. You know, Malia and Sasha, they have friends whose parents are same-sex couples. There have been times where Michelle and I have been sitting around the dinner table and we're talking about their friends and their parents and Malia and Sasha, it wouldn't dawn on them that somehow their friends' parents would be treated differently. It doesn't make sense to them and, frankly, that's the kind of thing that prompts a change in perspective." Source