A lot of christians like to say that their god has sovereignty over all decisions while claiming that man is morally responsible for any adverse results. There are a few variations on this theme; but it's all baloney. No one can be reasonably accountable for anything beyond his control. This idea was rather eloquently (I think) expressed in the children's story "The Little Prince." If a king gives one of his subjects a command that he cannot fulfill, whose fault is the lack of fulfillment? Naturally, it is the king's fault. It cannot be otherwise. I cannot reasonably be expected to perform acts that I have no power to perform. If you insist that all people have a "sin nature" and cannot be "sin-free," then it is unreasonable to expect them to be so. It doesn't matter that you say your god has an "alternate plan of salvation." If the so-called first plan is pure undoability, then the "alternate plan" is the real first plan.
The reasoning is inescapable. However, christians don't like to say that "accepting Jesus as lord and savior" (or whatever the verbiage du jour is) is the first plan. The conscience rightly says that that is wicked. So, they present a fake "first plan" that they think sounds better on the surface to quell their conscience. Something that would be an unreasonable requirement for Plan A might be taken as reasonable for Plan B. But I look more closely. The stated "Plan A" is impossible and is therefore only there as an illusion.