Of course the state recognizes marriage because it benefits society. See for example:
http://forums.anandtech.com/showpost.php?p=35249356&postcount=295
You are confusing marriage with the state's recognition of it. There is no reason for the state to recognize it at all, other than the reason I already gave, or other purely legalistic reasons which have nothing to do with gay v. straight. Marriage can exist as a social and religious construct, without state involvement. The state issuing a legal license is unnecessary to achieve whatever supposed societal benefits marriage confers.
What other conceivable purpose would the state have for issuing licenses to people who have formed personal romantic and sexual relationships, other than what I have stated? The relationships will exist regardless of state involvement, and procreation is a natural instinct.
Also, if your logic - that the state recognizes marriage to encourage procreation - holds up, then any country experiencing an over-population problem ought to cease recognizing marriage at once. Yet they do not. Every country, no matter how over-populated, legally recognizes marriage.
You do realize that is only relatively recently that women were allowed to own assets right?
In which legal system, at what time and what place? There are a variety of legal reasons to recognize marriage. The one I mentioned is the principle one. Laws regarding who can hold or inherit assets, dowries, etc. have varied considerably across cultures and over time. There has always been purely legal reasons for the state to recognize marriage.
So marriage exists so people can get divorced? 🙄
What an idiotic re-statement of what I wrote. No, "marriage" exists for personal reasons. The state's recognition of marriage exists so that IF people get divorced, there is an orderly process of dis-entangling and apportioning their assets. Divorce in some cases is inevitable either way.
It is entirely possible for 2 people to live together without co-mingling assets. Seems like marriage encourages people to co-mingling assets creating the problem in the first place.
It's hard to say what started the practice of co-mingling. Marriage undoubtedly existed as an institution before it was ever recognized legally. When two people have formed a lifelong domestic partnership, it makes sense as a matter of convenience to co-mingle, particularly as the people involved have no plans of ever splitting up. The problem, of course, occurs when they do, nevertheless, split up. Without state involvement, the parties have no recourse but to physically grab assets before their ex-partner does.
Also, if marriage is about dividing assets why do we let poor people get married?
Er, what? What would be the basis for disallowing "poor people" from getting married? They could acquire assets during the marriage, or have a very small estate to divide. Either way, it doesn't matter, because there is no harm in recognizing it.
To be clear, there are other reasons the state recognizes marriage, and predictably, they are all of a legal nature. For example, rules of intestate succession upon death, i.e. inheritance. Another is in the the modern world, the apportionment of public benefits.
The state legally recognizes marriage for purely legalistic reasons because the state's recognition is, by definition, a legal act with legal ramification. None of these things is particular or exclusive to straight couples.
Discrimination as to "marriage" belongs in the private sector, at the level of the church and the individual. There's no reason for it to exist at the level of the state. Enforcing someone's idea of what is a traditional marriage "under God" or any other ethos is not the function of the state, most certainly not the modern state.