According to Einstein (and no-one' yet proved him wrong) the Theory of Relativity does not preclude the possibility of time travel. But to avoid "the Grandfather Paradox" one is obliged to postulate alternative worlds or universes.
I go back and kill my grandfather. From the time I do that, or even before - if the world before that time is "leading up" to that event - that world is not strictly existing any more as the world I am existing in on my return to the present. It may be very similar to it, of course, because my time-travel act is insignificant in the big picture. Nevertheless, killing my grandfather would be something I do by "crossing over" into a parallel world.
Apply the same reasoning to free will. If parallel worlds physically explain away the paradox of time travel, it can also explain away the paradox of free will or choice. I make a choice that slightly alters the course of events as would have unfolded without that choice being made. But the world as it would have been is still real. It is the alternative world that gives my thought and act of choosing reality. If it were not, then it is the one world that dictates what I think and act as it "dictates" to the wind to break off a branch of a tree. Freedom of choice would have no meaning whatsoever. We would be robots cursed with a completely useless, meaningless "extra" (like an appendix) called "the illusion of freedom".
If there is plausibility to the general idea of parallel universes, then our real individual freedom to choose must extend to a collective freedom. Surely, we are "criminally" responsible if our choices fail to create a genuinely sustainable world (civilization) similar to the one I picture in my imagination and writings, the Syai world. Do we collectively want to fail - which will very likely mean a dead world, similar to the many as exemplified in the picture above? No; and leaving aside all moral consideration, to keep doing what we don't want is an act of madness.