I don’t intend to derail this thread, so it may be worthwhile to start a new one if this topic continues.
Civil marriage as I understand it is mostly a standardized bundle of contracts. Theoretically, you could jump through a bunch of hoops to get most of the benefits of civil marriage through contracts and legal forms. For example, by being married you can receive the estate of your spouse upon his/her death. However, doing this for all the things that a civil marriage covers would be very costly as you would probably need to hire a lawyer. Having a civil marriage to cover these things is much more practical.
There are some other things that a civil marriage gives which cannot just be given through contracts between the two individuals. For example, spouses receive exemptions from gift taxes. Also, with a marriage license, you obtaining priority if a conservator needs to be appointed for your spouse – that is, someone to make financial and/or medical decisions on your spouse’s behalf. To me, things like this make sense to give to those who live as permanent lovers. After all, what’s yours is your lovers, so that gifting should be exempt from taxation, and your spouse should be the one to make major decisions for you when you cannot.
For more benefits of civil marriage, check out
this page.