Over more drinks and more meals that I care to remember, I have argued with colleagues and friends about the existence of free will.
Drawing on recent findings in neuroscience, about delayed conscious awareness of actions and reactions, but also on a determinist view of causality, most of my conversationalists have insisted that there is no such thing as free will.
For my part, looking at events in ancient and recent history and reflecting on the sometimes surprising conscious life decisions made by others and myself (Martin Luther!), I argue with equal vigor that human beings have free will and that exercising it is what distinguishes us from other animals.
Of course there are various compromises possible: Daniel Dennett-type views that we should act "as if" there were free will and treat others the same way; William James; 'My first act of free will shall be to believe in free will:" Or Daniel Kahneman's implication that System 1 is automatic, while System 2 involves conscious reflecting.
But I've come to the conclusion that the belief or lack of belief in free will is not a scientific matter. Rather, to use the term created by the historian of science Gerald Holton, we are dealing here with 'themata'—fundamental assumptions that scientists and other scholars bring to the work that they do. And as such, the existence or the denial of free will, like the question of whether human nature is basically universal or inherently varied, is not one that will ever be settled. And so I have stopped worrying about it.