Why did God create people knowing they would go to hell?
Answer: First, God cannot do what is logically impossible. He cannot contradict Himself (e.g. God cannot create a rock so big that he cannot lift it). Similarly, God cannot create FREE creatures (e.g. humans) that do not have a choice to rebel against Him.
Second, there's a hidden assumption in this question that hell is a place so bad, that no one's existence could possibly justify being sent to a place like that. The details of hell are a mystery (those missing pieces). However, the pieces that are already together inform us that God is a God of holiness, love, mercy, and JUSTICE; consequently, hell is a place of justice (a place where wrongs are paid for). A place where Hitler will pay for his deeds, Ted Bundy will pay for what he did, and a place for everyone to pay for all the wrongs they have done here on earth who have not received God’s gift of salvation through Jesus Christ . We don’t deserve heaven. We deserve judgment, and hell is that place. Sinners will pay for their sins in hell, no more, no less than they deserve—GOD IS JUST.
"That servant who knows his master's will and does not get ready or does not do what his master wants will be beaten with many blows. But the one who does not know and does things deserving punishment will be beaten with few blows.”--Luke 12:47-48
It is very plausible that God created Man only potentially immortal. Thus, immortality is a state gained by grace through faith when the believer receives eternal life and becomes a partaker of the divine nature, immortality being inherent in God alone.
“For God so loved the world that he gave his one and only Son, that whoever believes in him shall not PERISH but have eternal life.”--John 3:16
Don’t disregard the obvious (Big Unequivocal Pieces of TRUTH) for the sake of the mysterious (small nebulous pieces). In other words, don't find clarity in ambiguity from what is unclear. Find clarity in ambiguity from what is clear.
If you try to understand and connect the small pieces that don't belong together before the BIG pieces, you'll find yourself confused, frustrated, anxious, and hopeless in the fog of mystery. On the other hand, those that look for and connect the Big pieces (of TRUTH) before they move on to the smaller pieces are rewarded with the fruits of wisdom--joy and serenity. These are just the benefits for this world. There is extrinsic value (beyond this world) as well.
We will never complete the entire puzzle of TRUTH in this life, but we all try. If you focus on putting the BIG Pieces together and allow meaning to flow from the BIG pieces to the smaller pieces you will get much further on your quest for TRUTH.
Wenham, John William. Facing Hell: The Story of a Nobody ; an Autobiography 1913-1996. Carlisle: Paternoster, 1998. Print.