There is nothing philosophically unsound with "everyone should have the right to marry the one person they love." Yes, it is somewhat arbitrary. I'd argue that I can't find a convincing argument for it being more arbitrary than "everyone should have the right to marry the one person they love, as long as they are of the opposite sex."
That's precisely my point: There really is no philosophically sound argument for simply allowing same-sex marriage. It's really just an utterly arbitrary personal preference. At that point, I really don't see why the arbitrary preferences of a minority should be imposed, judicially or otherwise, on the majority.
I've looked at it every way and I cannot see a single way in which gay marriage is an imposition on heterosexual marriage.
And it is no less of an 'utterly arbitrary personal preference' than straight marriage.