Agree with your thought that a threat should not be the impetus for morality, on every level. It's not even morality, if morality, of itself, isn't the driver. On the other hand, on a shallow level, it's not unreasonable to adopt the moral course, for fear of damnation, but, as I alluded to in another post, theologically, nobody escapes hell, for fear of hell. A person of faith is not a believer, for fear of hell, rather is a person in agreement with God. Such Bible warnings are not for the saved, the believer, and more involve complete disclosure truth and justice require. This is a more deeply spiritual discussion, involving finer Christian doctrines, not for here, perhaps suffice to say God is not interested in frightened devils. I would suggest Islam, for somebody who wants that sort of god, as long as everybody is creating their own religion, or lack thereof, here. But, for instance, it's not unreasonable that fear of being punished by the law prevents many people from criminal acts, an intelligent person, but one not very morally disposed, could forego behavior that could land them in prison they may, otherwise, engage in, were it legal. This, of course, does not make them moral people. As a matter of fact, an upstanding citizen can be a real scumbag, morally. But this type of fear is even good, practical, if it leads to less trouble among unregenerates, for the individual and society. A lot of things very bad for you you'd not do, for fear, so what's wrong with that? In any event, God is not looking for worship of the justice fearful. He gives fair warning, that's all. When you think about it, unregenerate man will have no excuses, when they stand before God, a lot more than meets the eye to what God is doing, that goes to justice, the dictates of absolute holiness, things impossible for the natural man to understand. Very good point, in any case, frightening, in a real sense, that the golden rule is not enough, that man is that wicked.I do not find this to be true. Usually it is religious people who take this pov in my experience. I find it a bit frightening that some people need a threat of eternal damnation to find morality.
1 Corinthians 2:14 But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.