First let's deal with the societal concerns. Without a doubt, the ideal environment to raise children is a stable, traditional family structure. This is the way we were designed to work. One of the cornerstones of this is traditional marriage. There is a reason this has been codified in law and enshrined as a sacrament. Since the beginning of recorded history, the natural pairing has been one man and one woman. And statistics have shown over the years the value of this unit. And while I, and many others, are not in the ideal group, and while there are many traditional families that are as dysfunctional as the Democrat nominating process, and even though there are committed homosexual partners that put many traditional families to shame, this does not change our societal obligation to find ways to promote this basic and (hopefully) holy union. And it may be a matter of semantics, but there is a line that we have to be careful not to cross. And that is that some unions are for the greater good.
But is it the role of government to do this? Yes and no. The states have always maintained the power to define marriage, subject to federal action when civil rights were violated, such as was the case of Loving vs. Virginia, which struck down bans on interracial marriage. (Thanks to Dave for the info) However, as with anything, the state can inadvertently, in the rush to do the "right thing", trample personal freedom and individual rights. Such was the case in the great state of Ohio when, in 2004, a marriage amendment was overwhelmingly passed (61-38%). However, despite my belief that it is best to define marriage as between a man and a woman, I voted against it. Read the text, and I'll explain:
In essence, this not only defined marriage, but also banned any legal status for any unmarried couple. I had at least one child by then and was not married. While I didn't worry, as I was sure the relationship would work out (wow, was I wrong there), I saw there was great potential for harm.
Article XV,Section 11.
Only a union between one man and one woman may be a marriage valid in or recognized by this state and its political subdivisions. This state and its political subdivisions shall not create or recognize a legal status for relationships of unmarried individuals that intends to approximate the design, qualities, significance or effect of marriage.
In the end, though, it comes down to personal freedom; the freedom for two people to choose each other, share their lives with each other, and to be together until the end. We must, as a practical matter, allow two people the right to make these decisions. We must remember that love is not defined by laws or morality codes.
And that's what makes this such a messy thing to begin with....