In the United States, you are not free to name anyone you want as next of kin. You can sign a healthcare proxy, but the two are not the same. If I wanted my boyfriend to be my next of kin, for example, under U.S. law too bad. I could not establish him as such. This is one of the reasons bans on same-sex marriage have been so problematic. Imagine a gay man whose family has abandoned him (obviously not having his best interests in mind) but who has a loving partner of 20 years. Because he cannot marry his partner, his hateful family members will be his next of kin. The U.S. system does not allow people to establish next of kin freely. You are mistaken that we have that right in this country.
My point was that it is completely possible for next of kin to be established by a private contract, but the United States does not allow this. I was responding directly to a poster who said that establishing next of kin outside of marriage was "impossible." I have proved this to be inaccurate by pointing to countries where this is in fact done, although a basic understanding of contracts makes it clear that the only real barrier to free establishment of next of kin is the government itself.