>Those that do not believe in the sanctity of marriage are entitled to his/her opinion.

You've stated your opinion, and acknowledged that others may disagree.

But you never argued for your opinion, or tried to give a reason why someone who disagrees with you should take your opinion seriouslly.

So let's have a go at it.

It seems to me that marriage is a cultural idea. It also seems to me, that where marriage catches on, children are likely to be born who are likely to think that marriage is natural (as opposed to cultural) which means marriage is nearly assured to persist in culture throughout another generation. Further, it seems to me that children in such a situation are more likely to grow to be healthy and well adjusted than children without two committed parents.

That explains very well exactly why marriage persists today: it has created an environment where it is very likely to survive.

My question is: why should I be more reverent of marriage than I am of other cultural phenomena like building a multi-level parking garage, making apple pie, or doing the Hokey Pokey?