Jason makes a good point: Edwards's gay marriage answer to the Times was refreshing. More generally, there's something appealing about a politician who is aware that one of his positions is based on subjective experiences.
That being said, I don't believe Edwards is being sincere in this particular case (nor do I believe his true position on gay marriage is based on his experiences growing up). In fact, I'm pretty sure he doesn't actually oppose gay marriage (in his heart, that is). And therefore his explanation, while textured and interesting, is also dishonest.
Frankly I don't have a huge problem with his lack of total honesty on this issue if that's what it takes to get elected. But to hype his answer by billing it as a representation of his newfound truthfulness ... well, that sits a little awkwardly.