Hospital visitation is a tricky one. I suppose you could have people register who gets to visit, but it would be unfair unless you required everyone to do this. I would be pissed if I a family member got in an accident and died alone while I pleaded with the hospital staff while people in traditional relationships are allowed in without the same registration.
Of course there is still the issue of determining what the correct resolution of those issues is, so we will likely have a situation of multiple 'standard' contracts, and people picking one without actually researching the differences.
This case was about getting a spouse's name on a death certificate. The DOMA case was about taxation at death (https://en.wikipedia.org/wiki/United_States_v._Windsor ).
OTOH, civil marriage in the US (the religious institutions sharing the name are separate concerns, even when they happen to coincide with a civil marriage) is in many respects not like a contract in the usual sense, since many of the legal effects are not to create legally enforceable obligations of one party against the other, but for the partners to agree to jointly share some treatment from, and as offered to couples by, the government. (There are some features of marriage that are either contract like, or which could be mimicked by normal contracts, as well.)
Forming a marriage under the laws of a state is more like forming a corporation under the laws of a state than it is like entering into a bilateral private contract.
There should always be an option to declare bankruptcy and start over (unless you were guilty of a crime, which is a debt you shouldn't be able to dodge).
For example, if someone decided to enter a slavery contract, they could always later declare bankruptcy and default and start over. However, an employment contract of 1-10 years probably would be treated differently.
Therefore using government to correct them is somehow immoral? Not sure how that follows (or if not that, what you are attempting to say here).