I'd like to direct your attention to a post I made a couple days ago on the subject.
If you look at our brains and our lives on a purely chemical level, then yes, free will in effect doesn't exist. The fact that you can think about doing something, then change your mind doesn't disprove his argument.
If a character in a novel begins doing something, then changes their mind and goes about doing something else, that isn't free will. The character was MEANT to change his mind, it was already written in the story that he would. He could change his mind a hundred times over the course of the book, but that doesn't change the fact that the book was leading to the same inevitable conclusion the entire time.
Now imagine that you are looking at life through the eyes of that character. You would probably figure that those choices you made were evidence that you in fact have free will because you have no awareness of the future.
It's an abstract thought but it does make perfect sense. Of course, we don't like to think of ourselves as masses of chemicals going through some enormous, complicated, but fixed series of reactions. And as far as any of us are concerned, we do have free will, simply because there is no possible way we could ever tell the difference between an illusion of free will, and true free will anyways.
It's actually an interesting thought experiment.
Even if true free will does not exist, that doesn't mean we are free from any accountability (to those who are using that as the basis for their arguments).
Like I said in the final paragraph of the above post, as far as we are concerned, we DO have free will because we have no possible way of knowing the difference between free will and an illusion of free will. For all we know, the entire universe we live in is nothing but a massive computer simulation like in The Matrix, but it wouldn't really matter anyways. It feels "real" enough to us, so as far as any of us are concerned this is in fact reality.
What I'm saying is that even if we don't have "true" free will, we are all subject to the same illusion, so we define that illusion as being free will. There is no freedom from responsibility for our actions. I would still consider someone a nutcase if they tried to justify murder by saying there is no such thing as free will and therefore he was inescapably destined to commit the crime.
Like I said before, it is merely a thought experiment. Whether or not free will is an illusion does not change anything. If EVERYONE sees the same illusion, the illusion for all intents and purposes, is reality.