It never ceases to amaze me how many philosophies deny the existence of free will. The big three: Calvinism, Materialism, and Islam.
For sake of this article, let us focus on Islam. In Islam, Allah predestines everything, even sin. For example, in Sahih Bukhari, Volume 7, Book 77, Number 611 (link), we read "Narrated by Abu Huraira The Prophet said, "Adam and Moses argued with each other. Moses said to Adam. 'O Adam! You are our father who disappointed us and turned us out of Paradise.' Then Adam said to him, 'O Moses! Allah favored you with His talk (talked to you directly) and He wrote (the Torah) for you with His Own Hand. Do you blame me for action which Allah had written in my fate forty years before my creation?' So Adam confuted Moses, Adam confuted Moses," the Prophet added, repeating the Statement three times."
Here, we see a dispute between Adam and Moses. Moses blames Adam for getting mankind kicked out of Paradise, but Adam basically replies with "how can you blame me for what Allah determined before I was created?" Now, if free will exists in Islam, Adam's response would be foolish, since he freely chose to sin, resulting in the Islamic version of the fall. But if free will does not exist in Islam, Moses could still blame Adam for his sin. Why? Because he had no choice either! The same logic Adam used against Moses, Moses could likewise use against Adam.
We see, then, how only if free will exists can it ever make sense to discuss it. The whole point of discussion is to arrive at an agreement on the truth. Yet, if free will does not exist, nothing we say matters; we are not free to change our minds, even if a good point is raised. It is like two robots arguing. Try telling your clock about daylight savings time! You can tell it "no, you're wrong by an hour", it will still insist on telling you the same time.
But though these discussions are illogical, they are also inevitable. Just as we are unable to change our minds about the existence of free will, we are unable to change our minds about discussing it. Yet, those who deny free will will inevitably walk away from the debate, regardless of how it went, feeling somehow intellectually superior to their opponents. But this is like believing you have the power of flight if you've merely been on a plane. But jump out and see if you stay in the air. If you don't believe in free will, how do you believe you have any advantage in anything you believe? Everything you believe could as easily be an error it was determined you would believe.
You see, then, how denying free will is utter folly. I believe denial of free will stems from a desire to deny personal responsibility. If I have free will and I fail, it is I who am the failure, but if I deny free will and I fail, it is not I who am in error, but it was predetermined that I would fail. It is easier to handle failure in a system that is rigged against you.
But the truth is, the system was never rigged against you. Not only do you have free will, but also a God who is judging how you use it. Ironically, He has rigged the system for you. See, not only are you responsible for every failure, but you have failed repeatedly. Yet, beyond all imagination, Jesus entered the battlefield. Unlike us, Jesus never failed. He submitted His own free will to the will of the Father, never once sinning. Because He never sinned, He never earned any punishments for sin. Nevertheless, He was punished quite severely. Why? Because we failed. We are due punishment, yet God would rather not deliver. Therefore, it pleased God to crush Him, putting Him to grief as an offering for our sin. Effectively, we swap verdicts. There is but one condition: Faith. Repent of your failures, confessing Jesus as Lord, and believing God raised Him from the dead. This will be the greatest choice you have ever made.