Sigh... once again... this says it better than I could:
Calvinism makes the author of sin and does not bring glory to Him.” This is another recurring accusation but those who use this as an argument have the same if not a greater problem. If God merely created man and chose them based on their foreseen acts of faith, as their position holds, and God knew some of these would choose hell, then why did God go ahead and create them to begin with? In other words, their eternal destiny is fixed by some kind of impersonal fate since the future cannot be changed if God already knows it. If whether or not someone chooses God is already known by God then the future is certain, correct? But the biblical view is that the future is certain because of the eternal plan of a merciful and loving personal God. The foreseen faith view is based on an impersonal determinism. Something is determining their future choice, in that scheme, but not God. So what is it? If God already knows the outcome, meaning the future cannot be changed, then the future is fixed and there is no real freedom. Their choice is determined. So why did God, then, go ahead and create them? The biblical and philosophical problems with the foreseen faith position, then, are much, much greater than with the biblical one. They appear to be trying to get God off the hook rather than taking a hard look at the Scriptures.
Furthermore, I would answer your question by saying that God is not the author of sin. Ordaining something like sin to take place is not the same as being the author of it. For example, God ordained the crucifixion to take place yet God cannot be blamed for the secondary causes which made it happen – the evil acts of men which carried it out. God ordained the evil of the most unjust act in history to take place…See the following verse:
“…this Man, delivered over by the predetermined plan and foreknowledge of God, you nailed to a cross by the hands of godless men and put Him to death.” Acts 2:23
So God, although ordaining it, cannot be blamed for it. As humans, we always choose what we desire most. God does not compel us to make any decision, and does not compel us to disobey. We do so willingly. All God needs to do to harden us is remove His grace and leave us to our free will.