"Free" will necessarily breaks causality, Jaime's desire for a sense of it that doesn't notwithstanding.
I think this is a semantics issue. I don't define free will the same way as you do, and therefore your declaration that it breaks causality is not necessarily true for anyone's definition but your own.
I believe you define free will as a supernatural ability - the ability to make decisions that ignore causality. I don't define it that way. I define it as the ability to make a decision between multiple options (as opposed to being constrained so there is only one option). Whether or not I would make the same choice if someone rewound the universe is irrelevant, since it's pure speculation that nobody can possibly test. What matters is whether the result of the decision was preordained or not. And I don't think we understand enough about the brain to be able to say, "yes, it was preordained with no option but the one that actually happened". Yeah, sure, we can sort of trace neuron activity, but we've only been seriously studying the brain for a couple of decades at most - and it's an incredibly complicated organ. You guys might be confident that what we've already discovered rules out free will; I am not.