I haven't read this long thread yet, but let me first agree with you. I don't believe in free will either. I believe in free "agency" -- meaning that I am responsible for my own actions. However, my will is not free. It is a product of a lot of things -- genetics, biology, environment. In the end, I cannot control my brain, because "I" am an emergent property of my brain. Freewill is an illusion -- but a very handy one. Now, on to how this matters:

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Because of these beliefs I am ethically off the hock if I kill / rape / steal etc.

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You are only off the hook, in that there is no "you" apart from your functioning brain. Un/fortunately, society will do things to either change your brain, or keep it from hurting their brains. So, you should use your free agency to try to adapt your brain in such a way so that soceity doesn't think they need to adapt your brain for you (or lock it up, or destroy it).