Some versions of determinism seem to be suggesting that individual human organisms can kind of be snipped out of consideration along their skin-line, and that all the details of the missing individual's behavior could still be predicted through knowledge of the individual's environment alone. If we know their society, what they were taught, what they personally saw and heard, in absolutely precise detail, then they would be entirely predictable automatons.
I don't think that vision is very likely at all.
A great deal of what generates our behaviors is internal. It's our desires, our emotions, our memories and our beliefs. And I'm not convinced that human internal states can be predicted with 100% accuracy, even in principle, simply by minutely describing external environmental conditions surrounding the person.
It may or may not be true that a person's observable behavior can be accurately predicted if we know everything about his/her environment, and also have full knowledge of his/her internal desires, beliefs, feelings and motivations at the precise moment a decision was made.
Let's assume that psychological entities like beliefs, feelings, desires and motivations are the kind of things that enter into causal relationships, or alternatively, that they are internal representations of neural states that in turn are causally determined.
The point is, is it really inconsistent with the idea of free-will to say that our decisions and actions are determined in some large and inescapable part by our own desires, motivations, beliefs and feelings? Isn't that precisely what free-will insists happens? What's the alternative to motivated self-determination? Jerking around spastically and convulsively?
I'm not convinced that free-will and determinism really need to be antithetical to each other.
I believe you are entirely on the right track in the last half of the post.
The only point I would have is that you seem to be concerned that being predictable removes your ability to freely do as you chose. Predictability isn't the same as predetermination. Predictability is local and temporary. That fact that we can predict a person's actions doesn't mean he isn't doing exactly what he wants to do, after thoroughly considering his alternatives and influences and making an informed decision to act in accordance with his wished. If you had all the information there was about his "input" and "character" you could predict him, and he would be fine with that. Free and predictable. If he has worked on his character and is proud of it, he wouldn't want it any other way.
But that doesn't mean that all eternity is set in stone right now. Because it turns out there are entities (us) who have the ability to understand how things work and what causes result in particular effects. And because we have a will and we want to exercise that will to our benefit (and to the benefit of those we care about) we can manipulate things to turn out differently than the unreflective clockwork mechanisms involved in determining the future of most systems would cause. We can predict results and change them at will.
These guys like to say that we are a clock too, which is ridiculous. A clock can't look at it's mechanism and decide it wants to run faster or slower, or stop and wait a while. It is a mechanism that can't see what the future holds and take action to change it.