President Obama has come out in favor of legalizing same sex marriage. This won't change anything right away. It will continue to be legal where it is and illegal where it isn't – which is most of the country.
Still, this may start some new discussion on an old issue. The United States is first and foremost a democracy in which we believe that citizens can decide many things for themselves without needing a government to do it for them.
There's a whole series of old jokes, one liners like: if you don't like cauliflower, don't eat it; it you don't like pool, don't play it; and on and on – meaning we don't need a government to tell us about these things. We are perfectly capable of deciding them for ourselves.
I believe same sex marriage of one of those things too. Often marriage, of whatever sort, is part of some religion. The Constitution is very clear on that point. The government should leave religion alone. The First Amendment says, "Congress shall make no law repecting an establishment of religion or prohibiting the free exercise thereof…"
That seems to me to say that you can marry as many people you like of whatever gender all at once and it's none of the government's business. Now what the church of your choice may have to say about it is another matter entirely.
As noted above, same sex marriages are against the law in many states. Let's hope Mr. Obama sowed the seeds of change.