[SteveA]

Most people would agree that free will seems to obviously exist, so it would seem the burden of those who want to discount it to supply some concrete evidence.

If our actions are simply a product of unescapable physically predeterminable interactions, then people should be able to predict relatively accurately something as simple as how your arm is going to move a couple seconds ahead of time.

Until someone can tell you what you're going to do a couple seconds before you're going to do it, it seems almost religious faith that free will doesn't exist.

It seems like attempts to demostrate free will doesn't exist occur with examples of things where people don't feel they were exersizing free will either. It's not unlike applying an external force to move someones arm and then claiming that they weren't able to control their arm.
My guess is that consciousness and free will exist as the quantum mechanical energies we see that exist in almost everything. We know very little about how they operate but can see the effects. So even scientifically it seems that there's little evidence to deny that free will exists. You mentioned chemical reactions but chemical reactions, especially organic ones as they are relatively weakly interacting are influenced by quantum mechanics, which places strict limits on how much we can predict or how detailed a view of things we can get.

If someone jumps off a roof, they'll fall. If you shine a light in someones eye, the iris contracts etc., but these aren't things people generally consider they can control via. free will. They need to demonstrate that they can accurately predict what decisions and resulting actions a person will make in the future if the claims that free will doesn't exist are to have a stable foundation, but they can't do that ... and if free will exists as quantum forces, there's no evidence yet that it will ever be possible.

(Though I do agree that we're to a very large extent a product of our environment. Larger than most people intuitively recognize)