Sanctiity of Marriage

Those three words are a huge part of the upcoming election. And almost all the presidential candidates are all for defining Marriage as a union between a man and a woman. But why? Who does it hurt to allow gays and lesbians to get married? Why shouldn't they? Is it just the homophobe inside them all or is there something I don't get?

If marriage needs a legal definition, define it as a union between two people. It hurts more people not to define it as a union between two people than it does to define marriage as a union between a man and a woman.