1. Our current society is formed around the idea that free will exists, and people are responsible for making their own choices. If humans do not have free will, then all advice, exhortations, commands, prohibitions, rewards, and punishments would be in vain.
2. In response to C's question, it is important to note God's frame of reference, in regards to time. That's because this particular argument forcibly constrains God into a certain time frame. Another popular argument, "What was God doing before he created the universe?", does the same thing. This is the point where those arguments fall apart; God doesn't fit into certain time frames as God exists outside of time.
The theologians teach us that God exists in "the eternal present". This is to say that every time of eternity exists in the present, for God. It is impossible for there to be a future or a past for God. Hence, it is impossible to talk about past time, in regards to God, which is what the "before the universe was created" argument tries to do. It is equally impossible to talk about future time, in regards to God, which is what the "God knows things before they happen" argument tries to do.
3. Also in response to C, you said "God has to be right; it cannot be any other way. It precludes all other outcomes there might have been." I just want to make a minor clarification, because that's technically not how omniscience works. If someone is truly omniscient, that person knows all actual scenarios and all possible scenarios.
That could make a good science fiction book. You know, a book about someone who knows all possible scenarios, but doesn't know all actual scenarios.
4. I find it interesting that Albert Einstein would be a Newtonian determinist. That's because Einstein sort of...um...disproved the Newtonian notion of how time works. That is, Einstein worked to show that time is relative, in direct contrast to the idea that time goes forward, in one direction, at the stable rate of one second, per second, for everyone and everything.
Of course, the world mostly still follows Newton's view of time (source: Back to the Future). And if we really want to get technical about it, that's Aristotle's view of time, in more modern scientific terms.
5. In response to Athena, I must protest against your portrayal of the Christian view of free will. There are some deterministic Christians, such as Saint Augustine (to a small extent), or the heretic John Calvin (whose heresy mostly centered around the issue of determinism. He held other heretical views, though). I would say the majority of Christians are not determinists.
Specifically, though, I must emphatically insist that Christ's life was not predetermined. The fact that Jesus was able to predict things ahead of time did not mean they necessarily had to occur. Jesus had three types of knowledge, one of which is called "knowledge of blessed" or "knowledge of divine things", which he received from his participation in the Beatific Vision. From this, he knew that he would suffer much and be handed over to his enemies. And, in fact, anyone who closely and correctly reads the Old Testament, like Jesus did, would know this fact. But the specific manner in which this was to happen was not determined. Jesus could have been betrayed by one of his other disciples, but Judas was always the most likely to betray him, seeing as he was the greediest, and he left the Last Supper early.
Um...that was kind of an info dump there. Let me try a different tack. The Christian philosopher teach us that two specific moments in regards to Jesus (Mary's acceptance to give birth to Christ, and Judas' betrayal of Christ) had to have chosen freely, because they would lose their efficacy if they were predetermined. Intellectually speaking, it's interesting that these two crucial moments in salvation history are almost exact opposites; one is accepting the will of God, while the other outright rejects it.
6. Here's a crux of the matter. What would you consider to be "adequate proof", either for or against the existence of free will? Clearly, examples of people exercising free will is not considered adequate proof, for reasons I don't understand. Has anyone brought up St. Thomas Aquinas' teaching that free will is a necessary condition of rational thought? For him, the argument isn't, "Does free will exist?"; the argument is more "Does rational thought exist? Yes. Therefore, free will must exist."
7. Anonymous asked how we reconcile the concept of free will with the idea that "God has a plan for everyone" and "everything happens for a reason". Let me answer by quoting the Book of Sirach. The Protestants removed this book from their version of the Bible.
In the beginning, God created humans, and he left them to follow their own wills. If you choose, you can keep the commandments, which will place you in God's favor. Set before you are fire and water; stretch out your hand to the option you choose Before everyone are life and death, and whatever they chose shall be given to them. The Lord's wisdom is immense; he is mighty in power, and he sees all things. The eye of God sees all that he has made; he understands every human deed. He never commands anyone to sin, nor shows leniency toward deceivers. (Sircah 15:14-20)This Bible passage actually explains a lot of what I've discussed today. Maybe I should have opened with it. Anyway, if you want a Bible passage which directly talks about human free will and God's knowledge, this is a good one. Note that the two are not at odds with each other here.