Marriage - A civil or religious institution?

The controversy over gay marriage makes me ponder the nature of marriage from religious and civil viewpoints. It appears to me that the definition one applies to marriage impacts one's position in the controversy. Blending civil and religious rules in the marriage contract gives rise to confusion. I believe any resolution of the matter requires separating the civil components of marriage from the religious components. One is the responsibility of the state. The other is a matter of personal conscience and religious choice.

How does one define marriage in 2010 American society?

Is it the institution society designates for the care of children?

The state adjudicates custody and support arrangements for children during separation and divorce proceedings;

The state also adjudicates custody and support arrangements between unmarried parents;

No license is required to have or raise children;

Single persons, married persons, family members and friends can be among those designated as legal guardians by parents, or the state.

Is it a civil institution, founded upon a civil contract?

The state requires two adults seeking to marry to get a marriage license.

On the other hand, many states not only recognize, but mandate common law marriage between adults who have cohabited for a set period of time. Persons who have never formally married have found it necessary to get civil divorces in order to terminate their arrangements.

The state differentiates between taxes for married and unmarried adults.

The state regulates estate disposition for all its citizens and differentiates between married and unmarried adults.

The state differentiates between unmarried and married adults in defining the rights and responsibilities of persons for their partners.

Is it a religious institution?

Legal marriages can be performed by civil servants and have no religious basis or by clergy under the auspices and rules of a specific religion.

Some religions ban marriage between one of their congregants and someone from another religion. The state recognizes such mixed marriages.

Some religions permit polygamy. The state rules polygamy illegal.

Some religions prohibit divorce. The state permits persons to get multiple divorces.

It appears to me that the state's definition of marriage is secular and contractual. Religions tend to expand on that definition and adapt it to their own dogma. Thus, I fail to see what possible justification religions have for interfering with the state's definition of marriage unless and until the state interferes with that religion's right to define marriage for its congregants.

And the state has ABSOLUTELY NO BUSINESS adopting the dogma of any religion as ITS definition of marriage and its benefits and responsibilities.