Suppose you were misguidedly to give your own child poison. The fact that you might think the poison you were administering was good for your child, the fact that you might have gone to a lot of trouble to obtain this poison, and that if it were not for all your efforts your child would not even been there to be offered it, none of this would give you a right to administer the poison—at most, it would only make you less culpable when the child died.
This seems like a "definition of right" quote rather than a moral statement. I'd rather just say "being certain that poison is good for your child makes you subjectively right, but not objectively right, to administer it." Or if those terms are already being used for something else, we can make up new words.
Then of course we might ask, for example: when determining if criminal action is appropriate, does it matter whether the criminal had a subjective but not an objective right to commit the crime? And that would be an interesting question. In absence of a context, it's pointless to discuss which of two things should be called "right".
Here's the new thread for posting quotes, with the usual rules: