Although the word 'marriage' definitely at some time was tied to a (Christian) religious ritual, the cultural concept and currency of 'marriage' has grown legs and run right outta Dodge. It's the word marriage and not the specifics of the ceremony that has the cultural currency. So - yeah - my arguement then, is more about that we should apply the word marriage to civil unions. The closest equivelant I suppose would be the year we talk about in the West - we talk in terms of AD/BC. I also use those terms. It's not that I am pronouncing that I was born 1,984 years after the birth of a child called Jesus - but that these terms have been pretty well culturally assimilated to the point that they are the most instantly recognisable, understandable, and international. Obviously there's no 'sacredness' about the use of the terms - I'm just using that as an exmaple of another originally religious-tied term that has escaped its roots and now exists independentally. (Don't get me started on CE/BCE (the 'secular alternative' to BC/AD). Just too confusing/ silly) Another example that springs to mind would be Christmas. Utterly devoid of meaning for a whole lot of people who nonetheless choose to get together with their families and eat so much meat they turn into meat-creatures (delicious) each year. So, the roundabout point is: 'marriage' can and does exist without religion - and it still manages to carry with it the idea of committment and devotion without having to based it around the premise of believing in a magical leprechaun with powers over fish and some breads.

So I choose option 2 in your list. Everyone, anyone can get married. I see where you're coming from where you say you don't think it's 'fair or even appropriate' that a couple divorce after 3 years should ever be 'married' - the fear that the cultural currency of marriage will decline. I'd say that that's not really something we can know, and it's easy and tempting to always follow a situation down its slippery slope to Sodom (oops, relgious reference) but it's also dangerous to project on how culture will work itself out from your armchair.

But I have a puzzling new question to add for any animal lovers out there: is committment a human invention? I'm pretty sure there are some animal species that are fiercy loyal to one/ a group of partners. It's a biological phenomenon and not a cultural invention itself. Giggity.

Marriage is the basis of family, born out of necessity for procreation and survival of offspring. The need for women to be supported during the physically disabling time of childbirth & rearing young children. Many cultures hold fast to the strict traditions of marriage, resisting evolution. Sati – an ancient practice followed by some Hindu communities but outlawed by the British during colonial rule of widows who were required to throw themselves on their husband’s pyre stil practised today. Historically women unable to re-marry after their husband’s death had no means of financial support. Arranged marriages, traditional polygamy of Islamic religion now mostly outlawed.
We live in the best times in the history of the world, which is not often recognised.
Evolution brings about systems that work better than before. Marriage still has a place. Union of 2 people to either share life experiences or raising of children in safe & stable environments. Laws are being changed frequently to recognise de-facto relationships. Division of property & parenting responsibilities are being divided more equally during divorce.
I think we can have it all. A society where if you so wish to marry and live co-dependently for eternity there is a place for you in our world alongside the single mother or father, the gay parents and the playboy mansion with multiple Barbie dolls.
I’m just so glad I don’t have to marry a man I’m told to then jump into the coffin with him if he happens to cark it before I do.. Which lets face, would likely be the case, as men just don’t last as long!