Despite the nonsensical nature of your example (I’m not sure what their difference in political philosophy has to do with her having the ability to prevent him from putting a sticker on the car), it doesn’t make sense to say they are both “full owners.”
“Joint ownership” does not imply “joint FULL ownership.” Indeed, what happens during a divorce? If they each have FULL ownership, why does one person keep 100% of the car, and the other gets 0%? Or, perhaps the car gets sold and they each get 50% of the proceeds? If they are both FULL owners, should they not each get FULL value for the car?
Same as above.
I don’t see how.
Impossible. You’re asserting that the collective owns the individual. See here (and the link for “these resources” as well) for an explanation of “inalienable rights” and why you cannot give up your ownership of yourself.
Absolutely. Everything would come to a halt, quite literally, because no one would be able to even breath without getting permission from everyone else to do so…which of course, they would not be able to grant such permission because they themselves would require permission from everyone else to be able to move their mouth and communicate that they grant such permission. So basically everyone would all die out in a matter of minutes from asphyxiation. (Although the more realistic scenario is that no one would abide by such a ridiculous arrangment.)
As explained above, obviously your friend couldn’t be more wrong.