From a purely scientific perspective the purpose of sex is to send one's gene's to the future via children. Gays can't do that so, once again from a purely scientific perspective, they are not right from a sexual perspective. This doesn't mean they are evil or loathsome but it does mean that redefining societies long term mechanism for having and raising children in order to placate gays is somewhat odd.
Liberals don't care about the feelings of the vast majority of Americans nor do they care about the societal consequences of equating the massively promiscuous gay lifestyle with committed monogamy--<19 8="" a="" average="" br="" cheat="" each="" ever="" every="" gay="" has="" heterosexuals="" in="" of="" on="" other="" partner="" people="" relationship="" sex="" spouse="" their="" typical="" while="" with="" year.="">19>
The liberal position on same sex marriage is based on liberals belief that hedonism is the best way to view life and that all that matters is short term pleasure.
Conservatives view marriage as both beneficial and sacrificial. To them marriage is usually about children and raising a family. Conservatives realize the true blessing in a marriage are the children. Marriages without children are not all they can be, sometimes through no fault of the partners, which is why we sympathize with couples who try but fail to have children.
Conservatives sacrifice their own personal pleasures for the greater good of their children and society. Liberals want to redefine marriage so that gays can feel that their massively promiscuous lifestyle is affirmed.