I think removing the gov't from marriage would be an excellent idea. No tax benefits, no immunity from testimony against your spouse, and the things that can be gained by proper contracts and legal documents would be fair to do so.
But the gov't has never had any business in marriage.
Visitation rights in hospitals
Legal claims for the loss of a spouse
Rights of ownership in property
Assumption of paternity regarding children
Parental rights
Survivorship rights to property jointly owned
Child support
Alamony
Just to name a few protections that marriage allows a spouse.