Terence- we seem to be talking about two different things here.
Each human being is the sole owner of his/her life and body. Owner, sovereign, authority... whatever word works for you. Sovereign is, of course, one with no higher authority over them. Without this individual sovereign authority, how does one have any right to self defense, for instance? Would not one have to get permission from whoever did have that authority?
Each human being has sovereign authority over their life, from conception. But not every human is able (or willing) to exercise that authority, of course. Infants, the senile, brain damaged, etc... all must be cared for by others if they are to survive. This is, ideally, a voluntary acceptance of responsibility by the caregivers, but does not confer ownership. And if there is nobody willing to care for them, they don't survive. That's just a harsh reality of life, even in the socialist welfare state.
There are a large number of possible voluntary arrangements and relationships, of course. We can delegate tasks, permission to perform certain things regarding our lives and possessions, but we do not thereby necessarily surrender our sovereignty. One must be the owner, the "boss," in order to delegate.
Many people are happy to have someone else responsible for some things or everything. Many "give" themselves to god, for instance. But how can they GIVE their lives or loyalty or possessions if they do not first OWN them?
You, or anyone else, can certainly disagree with me on any of that. But for me, I own this life and my body. I am responsible for it, my choices and actions. I am not responsible for anyone else, or their choices. And nobody else has any LEGITIMATE authority to either make my decisions or to force me to assume responsibility for others. Power to do so? All too often, but that is a completely different thing.