I've heard that in other countries, Australia is an example I think, cohabiting couples already have similar (if not exactly the same?) rights as married couples. This has apparently lead to an increase in couples getting married. The reason being, that there is no longer a disincentive to get married. Formerly, in some cases, if there was a large disparity in the capital or earnings/earning potential between the individuals in the couple, the one with the more capital or higher earning may have felt more reluctant to marry (only in some cases!)This sounds cynical because people should get married for the right reasons, because they love each other and are committed to staying together, but it is interesting that removing the disparity between the legal status of marriage and cohabitation has lead to an increase in marriages.
It is a bit 'nanny state', and call me a reactionary (a liberal one), but I really think this would be an interesting experiment in terms of making people more cautious about who they are spending (wasting?) their precious lives with. If cohabitation really were a commitment, people might put a bit more effort into their relationships instead of seeing them as possibly temporary and disposable. I agree that marriage is the correct option for a committed couple but cohabitation has been popular because it is cheaper than living alone, more convenient and you could always walk out if it went sour. This would change. People who don't yet feel committed could still stay over at each other's places whilst not actually cohabiting. People who don't want to commit will still have that option, it will just be more obvious (can only be a good thing!)
I think it would make people more aware of what they are doing and, perhaps, fewer people would waste their time with a partner whose actions are different to their words, who don't really feel any responsibility for the other person's welfare. Couples would still split up but there would hopefully be fewer children growing up in homes where the parents are not together. I am a single parent and believe that we can do a good job on our own but I still believe a happy two parent family is the best home environment for children.