You're not getting my point. I am talking about a better way of doing things, and used the UK as an example. Establishing the next of kin with a simple contract gives people the most free choice in selecting people they trust to look out for their best interest. U.S. law assumes closest relatives are best suited for this, but the reality is that this is not necessarily the case. There is nothing wrong with having laws that establish a default next of kin in the absence of a written contract stating otherwise, but establishing a next of kin that overrides the default can be as simple as a private contract.
For example, the government would ask this question: Does this individual have a next of kin contract? If yes, enforce that. If not, enforce the government-defined next of kin hierarchy.
That's right. And who gets the privilege is defined by who the next of kin is, which can easily be established with a private contract if allowed by the government (as in the UK). Any law that references "next of kin" would look to the person established by the private contract as "next of kin."
Why would you think it was "better" just because the government isn't involved in the actual paperwork? There is no proof that the UK does it that much differently than we do. Show exactly how they do it that is "better". They still have marriage, still have birth certificates, right? Issued by or at least kept by the government? So then they really just added something else that is very similar to our adoption of adults.
No, they just cannot be easily established by a private contract, not as easily as we currently establish our legal kinships via the government, and you have yet to prove or even give evidence otherwise. So far, you have really only shown that the UK has different laws than the US when it comes to next of kin, although in reality, that is only partially true.
Now, I think I may know where the confusion lies here (although it could be something else). I know that I say that legal marriage establishes a legal kinship, legal relationship, which it does, of spouses. It isn't a generic legal kinship relationship though. It establishes a specific legal kinship that comes with specific rights, responsibilities, benefits, and privileges. It is just like birth certificates, adoption records, and in some limited cases court orders/rulings establish the specific kinships of parent and child for people. These too come with specific benefits, privileges, and some responsibilities. Those specific kinships are best established via the government since the government is where those specific benefits, privileges, rights, and responsibilities come from. By law, those kinships have to be recognized in at least some cases, particularly in cases like employment and anti-discrimination laws or insurance and anti-discrimination laws. For example, if an employee has someone listed as their child in their employment records, and gets insurance through their company, then the company/insurance company must give benefits to that child if they give family benefits, so long as the child is legally the child of the employee. However, a person cannot simply claim someone as their child. An uncle cannot claim that their nephew or niece is their child, despite being legally kin to them, just to get employee health benefits for the child, unless the uncle is the legal guardian of the child (although that is a different claim). A neighbor cannot simply write down a child's name on a card or in a private contract and expect to have that other person's child covered under their health benefits just because they are claiming them as "kin".
Next of kin in the UK isn't even used as you seem to think it is. It is for those specific situations when there isn't someone else a person has that they want to have as their specific next of kin. And it is only really for medical purposes. It isn't legal recognition. It is very much like me listing who I wish to have notified on my medical paperwork, which is something I choose and can be someone besides my husband (in fact, the paperwork I just recently filled out at my doctor's office asked specifically if I wanted to inform my spouse of the results, then asked if there was anyone else I would like informed, nothing says that the spouse has to be the next of kin for medical reasons nor that it can't be someone else).