If we genuinely had free will, we would be able to act contrary to the laws of thermodynamics.

If free will is lost, then all other mental faculties become compromised. Reason, which many atheists love to cling to, becomes a delusion. Morality, even in its subjective form, becomes an illusion. Nothing you do, and nothing you think can be trusted. Sitting there, asking for evidence ad nauseum becomes an exercise in futility. Determinism fails most clearly in practice. Science tends to progress more or less by looking at the usefulness of its fruits: can an idea predict, can it explain, can it make sense of reality? And although the physical sciences proceed on a presumption of determinism. Determinism makes no sense of reality on every other front. It requires one to pretend to be deluded, despite everything in your experience telling you that you're not. Determinism is a failed philosophy.

Free will does not mean freedom to choose what choices you get nor what situation you're in. It means freedom to chose between the choices you are given. Saying you don't have free will because you don't get to be a unicorn is nonsensical. Saying you don't have free will because of death and disaster is nonsensical. The only time free will is ever compromised is in the face of mental and neurological disorders.

The brain automating many functions does not affect free will either. You can see this most clearly in a reflex arc. You touch a hot plate, that information goes up the arm, stops at the spinal cord, then the spinal cord issues the command to retract. All of this is immediate, it occurs subconsciously without the aid of the brain. However, you can still make a free and conscious decision not to drop the hot plate. The brain sends signals to the spinal cord, which override the reflex. Certainly, your body will do all things possible to get you to drop the plate, you'll feel the stress, feel the pain, but you have the final say. A clear example are the Buddhist monks of Vietnam.

Free will occurs first and foremost as autonomy over the body you are given. You control its movements and its thoughts. As a result of this, free will then extends into your environment. You decide how you behave in the world, whether you go left of right at an intersection.

When it comes to neuroscience, the famous catchphrase should never be forgotten: Correlation is not causation. Take depression for example. You can take an fMRI of the brain and see the difference between a healthy brain and a depressed brain. But that information doesn't tell you what is causing it. Are changes in the brain causing the depression, or is the depression causing changes in the brain. In the absence of a clear biological marker, there is no way to distinguish between the two.

I’m not convinced free will exists in reality. Whether it does or does not is not known for sure yet. However, I behave like it does and that’s enough for me right now.

I think free will exists to a point limited by the laws of nature and your circumstances. I can like white trousers but choose to buy brown ones because the white ones will get to dirty too soon in my job. If I am willing and able to wash them twice a day I can opt for the whites. It wholly depends on me. Of course, if you start to nitpick then you can arrive at a chain of facts and happenings that made you take our decision and then say it was not your free-will but an illusion of free will because it was biologically determined. (You are genetically lazy, or your upraising made you a useless home-maker). It is very tricky. From the point of view of the daily life of the individual and the society, as many times we cannot forecast what other people would do, or even what we will do under a set of circumstances, there is free-will, in the sense that there is uncertainty about the decisions.

However, that free-will exists or not does not necessarily imply there is a God or not in my opinion if you approach it from the previous point of view of causality. God could be not all-knowing or all-powerful.

What is illogical is to have an all knowing, all powerful being (a God) that has a plan for Humankind and the existence of free-will. If there is a plan, and he is all-knowing, then he knows what everybody is going to do for the plan to work. If he does not, then he is not all-knowing or all-powerful. Free-will, under the assumption of that kind of God, is just an illusion God gives to men because he knows the decisions that will be taken beforehand. On that line, it is all a bad joke because he knows who will end up in Hell even before they are born and who will join him in Paradise. All your actions are pre-determined by the master plan.

Tricky thing.