I will not go into the religious aspects of marriage since they are not relevant to the discussion. I will cover the secular aspects of marriage because they are relevant.
Since governments have been formed from the dawn of time, they have generally served a common purpose, namely the collective good of those governed — society. We enact laws to establish an ordered and civil society. Governments long instituted tend to incentivize behaviors that are encouraged and penalize behaviors that are discouraged. A case in point is murder. Most sentient beings acknowledge a universal right to exist — life. This is codified in our first founding document — The Declaration of Independence. We are endowed by our Creator with certain unalienable rights that among these are life, liberty and the pursuit of happiness. Conversely, the denial of another person’s life (murder) does not serve societies greater purpose of a civil society — if anybody could just go whack somebody at will. As a result, most levels of government (local, state, federal) establish severe penalties for the denial of that right. So what about marriage?
Since the beginning of time civil societies have been dependent upon the growth of society for maintenance of the society. We are all mere mortals and we don’t live forever. As a result, in order for a society to flourish, a sustained fertility rate has to be achieved. Most statisticians peg that number at 2.11 births per family. Failure to achieve that will result in the loss of that culture within the civil society. You may be surprised to learn that we barely achieve that fertility rate in the US and only with the advent of illegal immigration. Most of Europe cannot and does not, save for Muslim immigration. So how does the civil society attain a sustained fertility rate and continue to survive/thrive? ANS — incentivize those behaviors that will achieve that end result. Through the ages, nuclear families have statistically achieved the greatest success in this area. This is the prime driver for marriage from a secular standpoint. Now, on the other hand, if you wanted to tear down a society, by all means do everything in your power to destroy the institution of marriage.
Wait a minute you say, this is all about civil rights and fairness. That would be a fair point and the underlying basis for why the whole concept of how civil unions were started and why they exist in many states. Still, if you put full equality to a homosexual marriage over a heterosexual marriage, you are forsaking the original intent of why you incentivized behavior in the first place. Governments above all, are about furtherance of the governments. If you cannot sustain a civil society via procreation and a nuclear family, the society will die off.
The final point will be about couples who marry and never have children. Roger, got it. Still, it’s about a numbers game. You need sufficiently high numbers on the input side to ensure you meet your targets on the output side. Factoring in infertile or childless couples goes into that equation.
Of course could just accelerate the breakdown of the civil society according to the master plan of Dick Lamm, Former liberal Democratic Governor of the state of Colorado (starts at 2:00 timing mark) ;-)