Marriage obsolescence is a future event that might happen in the short term a few decades and in the long term a few centuries.
One argument goes like so: Marriage is a product of sex and child-rearing. In developed countries, people have fewer children, because they do not provide benefits on the farm, and because they take a lot of time to care for. People will have more interesting things to do in virtual reality, such as having virtual sex. Who do they have sex with? Other people, but also their personal virtual girlfriends. These virtual girlfriends will have artificial intelligence and will be used to personally relating with its user, and modeling the user's mind. And the virtual girlfriend will know the sexual tastes and daily affairs of the user more acutely than anybody else. With both sex and non-existent child-rearing taken care of, marriage will be functionally obsolete.
The rise of secularism and the increase of birth control strategies since the latter part of the 20th century and early 21st century, premarital sex has become less of a taboo. Having children out of wedlock has become more accepted as well as having children from multiple partners. The concept of the traditional nuclear family has become extinct. The role of the father has become "the sperm donor" and the mother has become "the child bearer", which by some people, especially religious people, consider this behavior very "barbaric" and "animal-like" in nature.
Many new birth control methods have been developed as well such as the use of nanobots in the uterus to stop the multiplication of cells in the embryo to create new life. Many religious community, especially the Catholic Church, will consider these nanobots a form of abortion and would pledge a ban on this technology, as well as preserving the sanctity of marriage.
Declining Interest in Children
What of children?
There's a good argument that populations will go down. There won't be children, because they won't be viewed as necessary.
Our intelligence so far is that the more technically capable a demographic is, all other things being equal, the fewer children they choose to have.
Why might someone not want to have children?
- Children are costly.
- Children demand time, which people are valuing very highly.
- Children are viewed as a burden on others, not just parents. Just ask movie-goers.
- Children attract criticism. Everyone has ideas about how parents should raise children. Social ills are blamed (and likely appropriately) on parents.
- There is no reward for raising children, beyond the adventure of raising a child itself.
A Foreign Policy article wrote  (paraphrasing from the article) "If people are merely asking themselves, should I have children or not, it's already too late." The society's population will go down. This argument makes good sense to this author.
One conservative response is to reinstate patriarchy: A woman's job is to stay home, and produce children.
Immediate ideas that come in response to dwindling population include:
- instate patriarchy, either institutionally or socially -- the idea is to get women to stay home, and take care of kids
- ban pornography -- the idea is to make having sex with women be the main
- ban contraceptives, or make them harder to come by -- more children, clearly
- financial incentives to families -- give money and support to parents raising children
With the exception of the last, this author views all of the above as both morally difficult, and pragmatically unlikely.
Considering the technology of the future, there are other opportunities:
- manufacture people -- babies birthed through artificial uteruses
- flesh obsolescence -- if people live in computers and siliconize, then lack of children is not a concern
- increase desire -- genetically or semiotically modify ourselves, to desire sex more
The issue is immense, and opens up a multitude of questions.
- What freedoms do we believe in? Should people be allowed to sexually stimulate themselves?
- Should women be forced to have sex? Persuaded to have sex? How about men? Should men be forced to have sex? Persuaded to have sex?
- How can children with no identifiable parents be raised? What will they come out like? Would people call them "human?"
- Who do we want to become?
- What is the value of raising children, for parents?
- What is the value of population, for a society?
- Will society force people to have children, persuade people to have children, or reward people for having children? Rewards can be considered both economically ("here's your check, breeder,") and social ("how wonderful, thank you for raising children for us!")
- What about voting rights, and cultures? Does one-person one-vote really make sense?
- What of national boundaries? Can a country with a very small population maintain its borders?
- Can pornography be put "back into the bottle?" Can it be re-stigmatized, somehow? (Would we want to?)
- Does society owe parents anything? If so, what does it owe, and how will it compensate?
- Are people without children bad? Or do they have to pay something? Is there a child-bearing obligation?
- If you perpetually had the body of a 19 year old, would you want to have children?
- What about "sustainability?" How would cultures negotiate with one another, to make sure that they weren't trying to out-militarize, or out-vote, one another?
- What is the future military value of human beings? Might human beings be obsolete, militarily? Conservative arguments are frequently worded in terms of national defence: If population has little correspondance with military value, then the question may largely be moot.
- Can an artificial uterus be developed? If it can, would it be legal to use one? Turned around another way, might it be illegal not to use one?
- The Insensitive Man: Chapter 1: If Only They Wear Mini-skirts We don't Need Flesh-and-Blood Women Any More!? -- a frank description of male sexual interest, and the image of women vs. the material woman
- Wikipedia:Artificial Girl 2 -- one of several computer games