This question is based upon flawed reasoning, since it assumes that we are in a position to critique God. Many who refuse to look into what the Bible says on the subject simply decide that God seriously erred in this area, so we should not put our trust in Him.
When God created the world, we are told that God examined it and declared that it was good (Genesis 1:31). This means that even the angelic world did not have evil angels or demons in it at that time. But by the time of Genesis chapter three, we find that Satan, in the form of a serpent, was tempting Eve to sin. Therefore, sometime between the events of Genesis chapter one and Genesis chapter three, there must have been a rebellion in the angelic world, with many angels turning against God and becoming evil. This rebellion was led by Satan himself.
Since Lucifer had been the model of perfection, what sort of sin led to his fall? His heart became proud because of his incredible beauty. Lucifer allowed his perfection to be the cause of his corruption.
