Personally I see no reason for the government to define marriage at all. Call them all "civil unions" (or whatever). You go to the courthouse, get your civil union paperwork, it's not official until it's signed (and notarized) and returned to the courthouse. Then allow religious officials to notarize them. Done. Then you are free to have just as religious or secular a "marriage" as you choose, with any other consenting adult.
Hell, I don't see much reason you shouldn't be allowed to enter into such a contract with
any other consenting adult, provided we could divorce the slate of rights and privileges afforded by a legal marriage from the sexual/family aspect. Because really, that's all a legal marriage is...a contract allowing for certain benefits and responsibilities. Call it something other than marriage, and allow for a person to enter into that contract with any single other party they choose (limited to one due to some of the benefits provided...allowing legal polygamy comes with its own fiscal problems, even ignoring societal problems).
As for states recognizing civil unions for homosexuals and marriages for heterosexuals,
in theory that could probably work. I'm not a huge fan of "separate but equal," but with a legal arrangement (like civil union/marriage) it
is possible to make actually make them perfectly equal (aside from social stigma, of course). If they provide the
exact same rights and responsibilities, it's something that might not be entirely unacceptable. At least from a utilitarian standpoint.
Then again, especially based on how the civil union thing has worked out in some states that have implemented it, it seems that the main motivation for keeping civil unions and marriages separate is so that the former can offer less benefits. So "separate but (not so) equal" lives on anyway.
While i have a little heartburn with gay marriage, i must admit that it is a red herring issue much like flag burning and prayer in schools. The issue of gay marriage brings out the ultra conservatives and the ultra liberals. The two political parties could care less about the rest of us.
It bothers me that a few red herring issues like gay marriage causes the government of this country to switch poles every four or eight years.
I'd argue that gay marriage (or the banning thereof) has more "real" effect on more people than flag burning or prayer in schools. As in, actual
legal and financial effect. It may not seem like a "real" issue to you, because it doesn't affect you.