I think I completely understand what you are saying. I´m just wondering how you get to making these rules.
I have no problem with acknowledging that it will always be objectively true that the subjectively bestowed purpose of the creator was the subjectively bestowed purpose of the creator. In the same way that it will always be true that I used the thing for the purpose I used it for. Neither, though, renders the purpose objective.
And here we are at the point where you point out how your own analogy is doesn´t apply here: We would´t ask a knife to perform in a certain way.
Ok. Let me try to break this down further. Nothing, regardless of its ability to make choices, can ever be good or bad without a purpose. The purpose in itself can neither be good or bad. Without a purpose, it just "is". However, purpose is the only objective standard to measure the goodness of the qualities a thing possesses. In regards to humanity, we are either created with a purpose or we are not. There is no other option. If a knife was created to cut, who is the knife to tell the creator the he/she was wrong for not making it for decoration?
Taking this further down the rabbit hole. Lets say someone invented and created a robot. This robot had feelings, emotions, dreams, and even freewill to make decisions. But the creator created this robot for the sole purpose of inflicting pain and suffering onto it. Because the sole purpose of these "painbots" are to suffer, pain and suffering would then be good qualities for this painbot. If a painbot did not experience pain and suffering but only joy and pleasure, that painbot would be discarded as defective.
But what if the painbot gets angry with its creator for creating them for such a purpose? Well, that painbot would be objectively wrong because, by definition, a good quality painbot is one that experiences pain and suffering. The greater the pain and suffering, the better the quality of the painbot. This would be objectively true regardless of the painbot's grievances because a creation cannot change its purpose. Well, you may tell the creator that it is wrong to create painbots and that it is wrong for painbots to suffer. In doing so, all you have done was made the creator's motive and the very existence of painbots subjective. However, the definition of a good quality painbot still remains unchanged because its created purpose has not changed. Perhaps in this scenario the creator was a psychopathic serial killer and this creator created hundreds of painbots so other serial killers can fulfill their twisted desires on a created robot as opposed to another human being? What if as a result of the creator's invention, it saved the lives of thousands of people to include your 6 year old daughter? Would you still hold to your objection?
But what if there was an authority that reigned supreme with no equal who made a law that made painbots illegal. It still doesn't matter because the purpose of the painbots remain unchanged. A good quality painbot is still one which suffers greatly. But what if this supreme authority IS the creator and inventor of not only painbots, but the creator of everything that exists! Because the grievances of a creation has absolutely no impact on its created purpose, no complaining or disagreement from anyone can change their purpose. If you simply "choose" to give yourself a purpose that disagrees with the purpose that was bestowed upon you by your creator, that choice would be factually wrong. You would be declared defective like a happy painbot.
When it comes to humanity under a Christian worldview, we are not creations by a simple inventor. We are creations from the supreme Creator of all that exists! Because of His unique authority, whatever purpose He bestows onto humanity is ABSOLUTE by default. This absolute purpose is the standard at which makes the objective evaluation of the qualities of humanity possible. Otherwise, we are no different than rocks.