Both sides are asking the wrong question. The right questions is: why is the government involved in marriage, a religious ceremony, in the first place?
Legitimate government promotes righteous behavior through rewards and punishes wicked behavior.
And if you ask what defines righteousness or wickedness, you know where I’ll point.
To protect children.
I agree that government shouldn’t be in the marriage-recognizing business. To answer your question literally: Initially governments just struggled to get basic census-like information. It so happened that, until very recently, the overwhelming majority of folks got married, as opposed to co-habited without marriage, and open homosexual relationships were unheard of. Once marriage started to offer certain GOVERNMENT-CONFERRED advantages, such as tax treatment, inheritance issues, etc., the long slide began.
“why is the government involved in marriage, a religious ceremony, in the first place?”
It gives massive control of the culture, either for good or ill.
The problem with the state’s involvement, at least in the modern era, is that the definition it uses to recognize the institution is simply whatever judges, pols or the majority thinks it is at any one time. And that’s it, and that’s all it will ever be. Combine that with the fact many have been conditioned to think marriage comes from and is defined by the state and you have what we have today. It was always a danger. Pope Leo XIII warned about it 130 years ago.
Freegards
Lots of reasons, mainly having to do with children and property, since the time of Moses at least.
Are you sure you thought this through? Maybe you are a Libertarian anarchist?
Why is society involved in marriage? Why is religion involved in marriage?
Marriage has been around since the beginning; before government. There are many things the government recognizes, promotes and protects that are inalienable, endowed by the Creator.
Government did not create marriage and therefore can not redefine it.
Not counting you and other anarchic moral pacifists there are two sides to this issue which mirrors many other issues of the day.
There are those that want to redefine and impose upon society some leftist Utopian concept of fairness versus those who want to maintain that which is time tested and successful -a result of the free marketplace of ideas and choices made freely by millions upon millions over the centuries.
Homosexual marriage is a leftist construct. To NOT oppose the left is to promote the left -pick a side.