redblueamerica.com

I agree with the first commenter. Why is marriage in any form the business of the government? But, nevertheless, it is, so let's look at it:

Supporters of traditional marriage argue that the traditional family structure is very important for healthy children, and thus for society. No argument there. But in what way does extending benefits to gay couples adversely affect traditional couples? And how is keeping the benefits of marriage from non-traditional couples good for society? The underlying assumption is that marriage can be somehow encouraged or discouraged by the government by the benefits (spousal rights, tax breaks, etc.) it offers to married couples. But who gets married just for the legal benefits? If the government has that kind of influence, wouldn't it just encourage unloving couples to get married out of convenience? That's not good for society. On a deeper level, opposition to gay marriage assumes that sexual orientation is a choice. It's not like a gay person is just going to decide to "go straight" and start a family because of how the government defines marriage.

Legal benefits or not, dedicated gay couples exist, and dedicated gay couples with children exist. That's not illegal. Since they exist, isn't it better to offer them the legal benefits which make their lives easier and more secure? Even if you think these families are less than ideal, why is it bad to help them out like any other family? Many kinds of straight-couple families are less than ideal, but they all get their benefits.

Ultimately, the state and federal governments do not define marriage in reality anyway. They merely define it as a legal classification that is used to grant or deny legal benefits. In other words, they don't define the concept, they only decide who gets to use the word in a legal sense.