I agree with you. We live in a great country and every one regardless of national origin, gender, political views, or sexual preference should feel free to self expression and the pursuit of happiness. If a gay couple wants to get married, why should society condemn this? What about interracial couples? Will we make a law banning these unions as well? I sincerely hope not.

The argument is much farther reaching than just gay marriage.  The real question is how much power do we allow the government to have.  Where do we draw the line between religious issues and legal proceedings?  Gay marriage is largely a religious issue.  Should the government be allowed to dictate religious issues?  The argument of plural marriage and underage marriage arises.  Some religions teach plural marriage.  Should the government be able to say they are wrong?  Why?  If they are consenting adults and they aren't hurting anyone, why should the government be able to dictate how they live their lives?  This is the downside of our legal system.  Each law effects others and each decisions has implications that reach much further than just the one issue at hand.

I agree with both of you about same-sex marriage, and in response to Post 2, I would make this argument. Same-sex marriages and "traditional" marriages both involve two consenting adults, who are mutually agreeing to enter into a legal contract in which both are equal partners. In case of polygamy, at least as defined by our legal system, this is not the case. One man married to multiple women is not an equal partnership, as it privileges the man. For that matter, polyandry would privilege the woman, or, depending on the situation, the man. Similarly, a child entering into a marriage with an adult (to cite another example of the "slippery slope" argument often made by opponents of SSM) is not an equal partnership for obvious reasons. 

I agree with you.  I support gay marriage.  But look at it from the other point of view.  If you allow gay marriage, where is the moral or logical basis for stopping there?  If you can say that it is morally/logically fine to have gay couples marry (because they should be able to be happy however they want), what is the moral/logical basis for saying polygamy is wrong?  

As I say, I support gay marriage, but I do not think that I can logically justify saying (even though I think this) that gay marriage is fine and polygamy is not.