The way marriage is set up presently, it is made for the needs of a majority, but there are many outliers.

Firstly, of course many people cohabit very happily for a lifetime, there’s no requirement to get married. They settle their affairs with bespoke agreements property contracts and wills. It works fine for them - it’s just a bit more complex than the standard package that marriage presents , but not a real problem.

Don’t want marriage, but quite fancy the tax benefits? In the UK you can opt for a Civil Partnerships which handles most of the outliers https://en.wikipedia.org/wiki/Civil_partnership_in_the_United_Kingdom

Bottom line -for people who want to get married, there’s marriage. For people who want to formally merge most of their financial affairs and tax obligations, there is civil partnership, for everyone else, there are bespoke legal and financial arrangements and contracts.

No compulsion, no loss of autonomy (other than mutually agreed) an D.C. certainly no slavery.

Good, eh?