Even if things are determined would it matter? Either I don't believe it and act as if I have free will. Or I do believe things are determined and act as if I have free will. Actions have consequences determined or not and that is what we base our choices on.... well that and ideology.
First of all, I don't see why it would not matter if free will is false, because it matters whether we believe what is false. Unless, of course, it does not matter to you whether you believe what is false.
Second of all, it is a confusion to believe that determinism and free will are incompatible. What are incompatible are compulsion and free will. And it does not follow that because my choice, or my action are determined (whatever that means) that either is compelled. Suppose that what determines whether I visit a certain restaurant is that it was recommended to me by a friend so that unless he had recommended that restaurant, I would not have visited it. Was I compelled to visit that restaurant by the recommendation? Of course I wasn't. I did not have to visit the restaurant because my friend recommended it. So, why would my visit not be made of my own free will?