I also agree that it's not JUST unmarried mothers that lead to disadvantaged children. It's more complex than that.
Oversimplifying that though, the reasons children of unmarried mothers are disproportionately disadvantaged long term is due to things like inequality in terms of gender pay gap, non enforcement of child maintenance, economic status of parents etc
The reasons why people are against conferring equivalent to married rights on cohabiting couples are numerous, personally I think it would be incredibly difficult to define and enforce (how are the dates ascertained & proven? How do you protect people from being defrauded by people who claim to have been in a cohabiting couple who weren't? What about people - and there's a few on this thread - who don't want to put their own assets at risk?)
Also given the many who already don't understand the differences between being married and cohabiting and who believe the many myths surrounding this I think it highly likely there would be just as many who wouldn't understand that by living with someone X amount of time or whatever is used to define a legal cohabiting relationship meant they were conferring rights on their partner which allowed them to claim a portion of assets accrued.
With marriage as a clearly defined, active decision both parties cannot deny that they agreed on X date to enter into the legal relationship.
Again - seen many times on the relationships board, people don't always move in together in an active, decisive way. The infamous mn cocklodger would benefit greatly from such a change in law and they tend to move in by stealth.
BertrandRussell when I've been on threads discussing this possible change to the law it's mostly been cohabitees in a later in life ltr with children from the earlier relationship wanting to protect their children's inheritances/uni funds that are most vocally against the idea.
People shouldn't have a legal union enforced upon them.
Multivac - depends on how you define commitment. If the law defined it as lifelong and permanent we wouldn't have divorce at all.
Calpop - there are women on this thread who most definitely fall under the category of unwillingly unmarried, or who seem quite obviously unaware of their vulnerability. There are also women who think they're covered by various other legal and financial contracts they've put in place - which is an improvement but can never completely replicate the protections of marriage, and there's some women who are genuinely better off not marrying as they're better off than their partner (though where does that leave the partner?)
Better education and information is clearly needed.
But I don't think forcing people into a de facto marriage, possibly against their will or knowledge, is the answer.