A much better idea...

Marriage is about love and commitment, isn't it.  And love is a good thing: indeed most people of any faith or none would say we should love each other.  And we should commit to that.  And that would be good for society.

So let's just say that everyone is married to everyone else.

There: problem solved.  That wasn't hard, was it?...

What do you mean, it would make the word 'marriage' meaningless?

That was rather my point.