I am starting to wonder whether the way in which ordinary people, including both undergraduates and scientists, assume free choices to have alternate possibilities doesn't simply mean that the phrases "free choice" and "free will" simply mean a kind of uncompelled choice or will that involves alternate possibilities. The kind of resistance that non-philosophers show to the idea that there can be freedom and determinism, the matter-of-factness with which they assume Calvinism to be a denial of free will, seems to be good evidence that this is just what the phrases mean. If so, then the philosophically interesting question is not about the compatibility of free will and determinism, but about the compatibility of responsibility and determinism. For while the phrase "free will" very plausibly means a choice that has alternate possibilities, "responsibility" does not simply mean something with alternate possibilities.
If this hypothesis about language is correct, the ordinary lnaguage claim "Freedom is incompatible with determinism" is trivial. The claim "responsibility is incompatible with determinism" is non-trivial and controversial. One way to see that it is controversial is that the word itself is pretty broad. We talk of "causal responsibility" by non-agential causes, and that does not imply alternate possibilities.
I think none of this really affects discussion between careful philosophers. Philosophers' use "free will" differs from the ordinary use here, I think, in that in the philosophers' sense of the word, alternate possibilities are not a part of the meaning.