[Dirty Name]

Marriage has been about children. Consider if a 70 year old couple were to get legally married, or possibly two younger people who have been living together for 15 years but never intend to have children. What's the purpose of a tax writeoff or special legal treatment if they happen to file a form or not?

So to solve this problem, you want to throw the baby out with the bathwater? Why not just admit that NO government solution is going to be perfect, but strive for the best possible solution - the one that makes the most sense economically, socially and legally?

The only reason marriages were created in the first place was as an attempt to create a stable family unit

You seem to understand the basic concept, but then you point to anecdotal evidence of "families almost destroyed by family law" while forgetting the vast majority of families that are obviously helped by it.

What's the purpose of a tax writeoff or special legal treatment if they happen to file a form or not?

The purpose is to give additional support to the institution of marriage. Contrary to what some seem to think on these boards, marriage is NOT necessarily a religious institution - it's simply the most logical arrangement for biological parents to form a family.

It's not impossible for people to get married privately and sign some marriage contract indicating what commitments they have

Impossible? No. But a generation from now, the lack of government acknowledgement of marriage would most certainly result in a lower percentage of them taking place in the first place. Government recognition acts as an anchor for the institution, particularly in those relationships that aren't centered around the religious notion of marriage.