Arguing against same-sex marriage based on the “definition of marriage” is problematic.
Arguments based on the “definition of marriage” could refer to two different things: a traditional definition or a legal definition. I’ll address both.
(1) The argument based on the traditional, dictionary definition of marriage.
This is not a useful or valid argument. Dictionaries were not created ex nihilo. Definitions arise from the way we, as a society, use particular words. It is backward to argue that our culture is constrained by the definition of a word. Human society decides how a word is defined; human society is allowed to change the meaning of a word. Granted, a majority of people in the U.S. right now want marriage to mean “a union between a man and a woman.” But that has nothing to do with any inherent meaning in the word itself. Definitions are changeable.
(2) The argument based on a legal definition set forth by a state.
Gay marriage really should be a federal issue, based on the Equal Protection clause of the 14th Amendment, which of course trumps all state laws and state constitutions. See the supremacy clause. The federal constitution is superior to all state constitutions.
If one believes there is a federal constitutional right to same-sex marriage, then a state ban on same-sex marriage is unconstitutional and illegal.
If one does not believe there is a federal constitutional right to same-sex marriage, then a state ban on same-sex marriage is not federally unconstitutional. But you must then ask: does the state ban same-sex marriage via a law, or via the state constitution?
(a) If the state bans same-sex marriage in its constitution, then that’s that. (If, of course, you believe there is no federal constitutional right to same-sex marriage.)
(b) If the state bans same-sex marriage only via a regular state law, then you must analyze the state constitution and see if the same-sex marriage ban violates the state’s constitution.
My point is that the issue of same-sex marriage is a constitutional debate. If you are against same-sex marriage, it’s because you don’t think there’s a federal or state constitutional right to same-sex marriage, not because you think the “definition of marriage” doesn’t allow it. The “definition of marriage” has no useful role to play in this debate. Arguments based on the “definition of marriage” only blur the issue, and it would be more helpful if such arguments weren’t made. The debate turns on the interpretation of federal and state constitutions.
With respect to (1), I agree that we shouldn’t be constrained by the definition of a word, but I think people are averse to actively changing definitions, as opposed to letting the definitions change around them. (If anyone can change definitions without consensus to suit their needs, what good is language?) When definitions change, they do so gradually and generally not as a result of a specific movement.
I think the Fourteenth Amendment argument is strongest, but that’s because I believe in a Constitution that’s alive, rather than one frozen in the Eighteenth Century. I think, in a few generations, we will have a Brown v Board-esque decision agreeing with me. But we’ll need to have our Plessy v Ferguson first and, given the current state of the Court, it doesn’t look like it’ll take too long to have that happen.
On its face, the 14th Amendment looks like it should guarantee complete legal equality to gays and lesbians, as well as to minorities and women (i.e., no need for a separate Equal Rights Amendment). But courts seem reluctant to read it that broadly, perhaps because the intent might have been only to provide full citizenship to African-Americans (in conjunction with the 13th Amendment). So I have trouble believing that a court would buy an argument based on the 14th Amendment. But maybe if enough lawyers argue cases that way, someone might bite.
Whenever I see people using a dictionary to define anything, especially in the context of legal issues, I cringe. Dictionaries aren’t written by judges or lawyers, after all.