Straight marriage will be less meaningful if gay marriage were allowed; the sanctity of Britney Spears' 55-hour just-for-fun marriage would be destroyed.
Gay marriage is not supported by religion. In a theocracy like ours, the values of one religion are imposed on the entire country. That's why we have only one religion in America.
Children can never succeed without a male and a female role model at home. That's why we as a society expressly forbid single parents to raise children.