Is RA an alternative to marriage?
Not for me.
I got married right out of university. Some of our friends though we were mad - it was more counter cultural than shagging around, in our early twenties!
I spent 9 years of the next decade TTC, pregnant, in post-partum recovery, or breastfeeding and co-sleeping. I wouldn't have been able to go 'loving' other people - it wouldn't have been safe for my unborn children's health, nor practical. And between establishing careers and raising a young family and renovating a house there wouldn't have been time for DH1 to, and also spend time with us (putting emotions aside for a moment).
And then he got cancer. It was important to both of us that I had next of kin rights. That I knew him so well and we had so much trust and love that I could care for him through to the (way too young) end of his life. (I wonder where 'lovers' go when the person they used to have sex with has no sexual function after chemotherapy...)
And inheritance rights and bereavement benefits (only paid to married bereaved people) helped me to continue to raise our children alone.
So my experience is not that marriage is failing as an institution. When one marries the right person, it works really well to give financial and emotional stability.
When I consider whether RA is an alternative for some people... I think only really where someone doesn't have the biological restraints of TTC/pregnancy/birthing injuries - so people who don't want kids, or their kids are grown up. And the time constraints of real adult life - working, caring for elderly parents, the fact that it takes two full time salaries to afford the rent or the mortgage in the U.K., and all that, means that I suspect it will only really work for either those who have a lot of money, or who are happy with a very alternative lifestyle where they don't bother with mortgages and pensions and all that. And finally, I hope people engaging in this kind of lifestyle for the long term think about what will happen when they're ill or old and unable to have a healthy sex life any more.