1. Natural rights require that they be "inalienable."
2. If natural rights require that they be inalienable, then one must demonstrate the existence of a right that is incapable of being alienated in order to even consider the existence of a natural right.
3. Since no one has demonstrated the existence of a right that can't be alienated, natural rights do not exist.
Am I close to correctly stating your argument? If I'm off base, please correct me by restating the argument.