Homosexuals do have equal protection under the law: they have just as much right as a straight person to find a member of the opposite sex and get married. There is no discrimination regarding marriage; everyone is allowed to get married, regardless of your sexual orientation.
The question is: Why is the government involved in marriage *at all*? The answer: Marriage between a man and woman is supported by the "state" because it fosters the continuation of the population, and thus keeps the state strong (as opposed to non-existent). As homosexuals by natural law can not reproduce, there is no need for the state to encourage homosexual marriage.
Marriage is recognized by the "state" and provided a financial benefit to encourage something which strengthens the state -- no different than farm subsidies, or, by contrast, no different than the lack of federal stimulus for the buggy whip industry.
If the Federal government should begin to support homosexual marriage because they don't want people to feel left out (which they aren't -- anyone can find someone to get married to...no one is prevented from marriage, except my age), then why not just expand it to polygamy? Why shouldn't I have a traditional polygamist marriage, create my harem and have the same marriage benefits for all of us, because we all love each other...and in fact may have a more stable home, because the loss of one member is not 50%, but a lesser percent of the marriage, and thus of less impact?
<pours gas, strikes match, flings it, runs away...>