I believe in determinism, that action leads to consequence and that there are basic inviolable rules to the universe that direct this cause-effect cascade. Human actions happen to be a part of this cascade, simultaneously causing and being caused by the surrounding environment, not being independent of them.
However, that doesn't invalidate free will. Just because the future is predetermined doesn't mean that it matters that it's predetermined. You can try to predict the future, but by predicting it you allow yourself the possibility of changing it, therefore making your prediction moot. If you know the future and change it, then the future you knew wasn't really the future.
So is there really any difference between the future being the result of our conscious decisions of free-will independent of the laws of the universe, and being predetermined but unknowable? If you can't know the future, then why does it matter whether or not you can change it?