[ceptimus]

It seems to me that you are defining "free will" and "decide" to mean something different to their normal usage.

The driver of a road vehicle can decide to drive on the left or right side of the road (and it would be a good decision to choose the same side as everyone else in whatever country you're driving).

But it's ridiculous to suggest that a railroad locomotive driver decides to drive along the centre of the rail track. There is no choice in the matter - if the driver chooses to make the locomotive move then it is constrained to move along the track.

I think it's the same with determinism and free will. I believe that the atoms that make up our brains are constrained by the laws of physics. If a supercomputer knew the exact configuration of the atoms in my brain (maybe it would need to know quantum states too - which introduces problems, but lets ignore those for now) then it could predict my 'free will' decisions with certainty.

I might believe that I've made a free will decision to have cornflakes for breakfast rather than bacon and eggs, but the supercomputer predicted that I'd make that decision hours previously.

You may say that I still made the free will decision I thought I made - after all I am eating the cornflakes - but I think it would be more correct to say that I was constrained to "make the cornflake decision" - and so it wasn't what an ordinary English speaker would call "an act of free will" and not really even a "decision".