Personally, marriage should just be outlawed. If one wants the "experience" of the event then issue a certificate that also includes "But one get one free" coupon for an IHOP breakfast.
If this was done then - consider the revenue that would go back into the tax base if such was not a societal institution. Without those tax breaks it sure would make some folks think of having a child for the sake of saving a marriage, or popping out another so that can save some money.
I think even civil unions are wrong as it does exactly what the laws (or intends to do) what constitutes legal representation of sorts by a significant other, all which could documented in a living will. For insurance, and all other matters, forms should just be modified - and living wills be used as the legal aspect to give whatever coverage etc.
Thinking of additional positives - we no longer would have "divorce courts" as such, dissolving and getting into another relationship easy, even child custody cases would be better in the long run I imagine, and there would be no such as polygamy...
Whew that
varnish must of gotten to me today...