Marriage is a personal or religious arrangement, it is only the states business as far as it is also a legally enforceable contract. It is fundamentally unfair that people agree to a set of legal terms and cultural expectations that ideally are aimed to last a lifetime yet the state messes with the contract beyond recognition in just a few decades without their consent.
Consider a couple marrying in 1930s or 1940s that died or divorced in the 1980s. Did they even end their marriage in the same institution they started in? Consider how divorce laws and practice had changed. Ridiculous. People should have the right to sign an explicit, customisable contract governing their rights and duties as well as terms of dissolution in it. Beyond that the state should have no say, also such contracts should supersede any legislation the state has on child custody, though perhaps some limits on what exactly they can agree on would be in order.
Such a contract has no good reason to be limited to just describing traditional marriage or even having that much to do with sex or even raising children, it can and should be used to help people formalize platonic and non-sexual relationships as well. It should also be used for various kinds of non-traditional (for Western civ) marriage like polygamy or other kinds of polyamours arrangements and naturally homosexual unions.
Warning: First Read Everything Here, only participate or read on if you are sure you understand the risks.
Based on the commentary and excerpt Federico made on studiolo, I've added the book Nudge: Improving Decisions about Health, Wealth, and Happiness by Thaler and Sunstein to my reading list. Since the book seems relevant enough to this site and has been mentioned before, I may eventually write a review. The post by Federico is made up mostly of excerpts from Chapter 15 of the book "Privatizing Marriage".
In addition to this I recommend reading the following excellent essays:
The reason the particular topic he talks about caught my interest is because the proposed solutions by Thaler and Sunstein seem somewhat similar to the one I argued for...