If marriage is an economic status recognized and protected in law, then it can end up conferring benefits on heterosexuals that homosexuals would be prohibited from taking advantage of. These benefits could include joint tax returns, access to health insurance or other spousal benefits, the ability to have intestate succession pass to a surviving spouse if the decedent spouse had no will and other benefits.

In that case, it is a socioeconomic benefit that is being denied to a group of people on the basis of sexual orientation. This, based on my understanding of the Substantive Due Process Doctrine (though let me caveat that I disagree with the doctrine as a matter of strict legal construction), is unconstitutional.

Let me digress for a second: I think that there is no Substantive Due Process implied in the Fourteenth Amendment but I also am against having the Tenth Amendment be seen as simply a "truism". If such matters could actually be devolved to the states without the Federal government getting involved, I would prefer to see almost all the "hot-button" issues decided at a state level. However, I know that this doesn't work, Congress sticks its nose into anything and everything it can and as a result the Substantive Due Process Doctrine is a necessary check on the grasping hands of Congress.

There. The point is that whether or not you like the Substantive Due Process Doctrine it's there now and there's no way to put the genie back the bottle.

Conversely, if marriage is a religious institution then the government really shouldn't be recognizing it because it has little to do with the government's function (to defend the polity from external and internal threats to their continued physical existence and their lawful property).

The fact that marriage is viewed by the government as a non-religious institution, but rather a socioeconomic institution, can be seen from several indicia:

1. Although a religious ceremony may be performed as a means of witnessing a marriage, it is possible to get married at City Hall or through non-religious ceremonies (something atheists and agnostics do all the time).

2. The government also hands out divorce certificates. I am not aware of many churches that perform divorce ceremonies as a way of solemnizing the end of a socioeconomic union. Church dispensation may be granted in some cases, but the only religious system that I can think of that has a formalized religious divorce procedure is Islam. Say "I divorce you" three times in front of the requisite number of witnesses and the divorce is official. Ironically, it is fundamentalist Christians (and Mormons, who aren't technically Christian) who are the most up in arms about gay marriage, yet Christ said that divorce should not be allowed when commenting on the laws of Moses permitting divorce.

3. The government does not ask if an individual has the proper permission to remarry after a divorce. Catholics are granted divorces even though the Catholic Church prohibits them, and Muslims can get divorces even without following the Quranic teaching on the matter (saying "I divorce you" on paper once is enough). These individuals may still be considered "married" by their faiths, and a subsequent remarriage would not be recognized (they would be "living in sin" or "committing adultery" or at a minimum, be taking a second wife without the permission of the first). However, the government doesn't care if the pope or an imam recognizes a previous divorce.

Is that a satisfactory answer?