If determinism were true, in the radical sense that all moral choices are predetermined by hard and fast rules—on the order of the laws of physics—then free will would not exist.
This is assuming the strong implication that the states of mind governing choices were forged in the Big Bang and that we are locked into a Grand closed scheme. Successive states of that system are purported by strict determinists to be iterations on an initial state and immutable.
In that case, Nagel’s “moral circumstance and luck,” though seemingly capricious, would also be determined by “The Grand Equations.”
It could also be argued that Frankfurt’s First and Second Order Desires were completely predetermined—eliminating the wiggle room given for free will afforded by his mechanic of Second Order Desires. As a consequence, choice is but an illusion.
I do not subscribe to the notions or mechanics of moral determinism, after Dennett and Monad, in the sense that evolution has given conscious entities (humans and dolphins among them) a capacity for novel responses to system dynamics.
In effect, any closed system can be changed via interjections of acts by conscious entities—even to the extent that they are non-responsive, capricious, contradictory, or redefining. In that sense, the notion of moral predetermination is untenable. Moreover, Heisenberg taught us that to observe a system is to change it, and Godel taught us that despite the axioms that define a closed system, there exist true statements about the system that are not derivable from those axioms.
Therefore, Uncertainty and Incompleteness prevail through a form of Kobayashi Maru maneuvering. While physical laws are determined, consciousness is unrestrained and—QED—free will reigns.