“Physical determinism” (hereinafter “determinism” [or 'hard determinism' - GT])
a partial and unprovable hypothesis about the history,
present state, and future of physical bodies and force fields
in the universe, including the physical aspects of mental
states. The hypothesis is that every physical state of
affairs at any point in time is the causal product of two
things: (1) an immediately prior physical state of affairs
and (2) the laws of nature. “[D]eterminism” is the thesis
that “a complete physical description of the world at a
given time, together with a complete description of the laws
of nature, entails every truth as to the state of the physical
world at later times” - or earlier times, for that matter. If
determinism is valid, it means that with sufficient
information about the world and sufficient knowledge of
the laws of nature, one can both predict the future and
derive the past because every physical state of affairs that once existed, now exists or will exist in the future is
inexorably dictated by what precedes it. (Peter Westen, 'Getting the Fly out of the Bottle: The False Problem of Free Will and Determinism', Buffalo Criminal Law Review , Vol. 8, No. 2 (January 2005), pp. 599-652: 603-4.
Free will - Christian style
“Strong free will” is an ancient and popular hypothesis
about the causal origin of purposeful choices on the part of
persons. Purposeful choices can take the form of objective
conduct observable by third parties (e.g., purposeful actions
and omissions) as well as subjective events that can only be
experienced on a first-person basis (e.g., mental efforts and
mental vows). In either event, “free will” is the hypothesis
that purposeful choices are a feature of an individual’s will,
and that an individual’s will itself is not caused by
anything but itself. This is not to say that the free-will hypothesis denies the existence of conditions of, and
influences upon, choice. A dinner guest, for example, who
chooses to accept a second serving can do so only if he is
alive and conscious, and only if he is offered a second
serving; and his choice may well be influenced by hunger,
taste, and affection for his host. But free will hypothesizes
that regardless of whether the person ultimately chooses to
accept the second serving, he could have chosen
otherwise—that is, he would have chosen otherwise if he
had wanted to, and he could have wanted other than what
he actually wanted. As Robert Kane puts it,
[Free will is the assumption that] (a) it is “up to us” what we
choose from an array of alternative possibilities, and (b) the
origin or source of our choices and actions is in us and not in
anyone or anything else over which we have no control. (Peter Westen, 'Getting the Fly out of the Bottle: The False Problem of Free Will and Determinism', Buffalo Criminal Law Review , Vol. 8, No. 2 (January 2005), pp. 599-652: 605-6; Robert Kane, Introduction to Oxford Handbook, supra note 13, at 3, 10. )
Of course, there is no canonical, consensual definition or understanding of the terms 'hard determinism' and 'free will'. But I don't think I need this in order to answer your question. If hard determinism is (taken to be) the position defined above, then it has nothing to offer Christian free will as this has also been defined.
If every choice or action is 'inexorably dictated by what precedes it', then 'it is not “up to us” what we choose from an array of alternative possibilities, and (b) the origin or source of our choices and actions is not in us [but is in someone or something] over which we have no control. Our choices and actions are the products of inexorable antecedents stretching back indefinitely and certainly before we even came into existence as agents.
Predestination might live comfortably with such a view but I think for the majority of Christians we sin and it is in an important sense 'up to us' that we do so. It is problematic to harmonise this with hard determinism - difficult to see what fruitful dialogue there could be between free will Christians and hard determinists.
I am not pointlessly, dogmatically and incredibly trying to lay down the law about the essential nature of hard determinism or of free will. My point is simply to suggest that it is this kind of picture that in your terms 'puts Christians off hard determinism'.
I confine myself to that limited question. Nothing in my answer reflects my own religious views.