Marriages as "Adversary Relationships"

[tadeus]

I think this is definitely part of the idea of marriage, or any living situation with another person, as adversarial.

This is what everyone should think - but what is the reality?

If two beings want to swear allegiance to each other in some form, why does it need a document from a public institution?
Why this needs any kind of registration?

A marriage certificate primarily records the joining of two merchant ships to form a joint merchant fleet under a common flag.
This creates a new legal entity called 'spouses'.