I think free will does not exist. Because I believe in causality. I believe that everything in the world is caused by something else. When I see a computer placed before me, I know that somebody did place this computer here. When i see the electrons on the screen forming shapes, I understand the reasons behind it are the signals going in from the CPU and the hardware manufacturing based on mathematical laws. In other words, there is a deterministic law-governed sequence of events as the cause of any event at any time and place - the sequence will start right from the beginning of time to the event in question.
There is nothing that I can think of which will _prevent_ me from including human caused events in this set of "explanable" events.
What one thinks he *wants* to do, has a perfect scientific reason on the the level of atoms (or whatever is the lowest level, say, quarks) for him wanting to choose this particular thing.
[Ofcourse, the uncertainty principle tells us that determinism doesnt work at very low levels, but we can hardly attribute free will to the undeterminism of this kind.]
We get a hint of this lowly determinism at higher abstract forms of realities as well. For example, me wanting to choose to eat chocolates can be explained by my experience in life, where I was exposed to a lot of chocolates, and the moods I was in when I ate those initially, the emotions expressed by those eating chocolates around me, the psychological game I was playing at that point, etc etc. Most of the behavioral patterns (in other words, free will based choices) can be easily traced to some experience, or genes.
My being good or bad can be traced to events that happenned to me. All of my behavior, from small to the large, is a result of what I observed in early childhood upto now, and what I was told. Apart from the genes ofcourse.
Now I want to my right hand to the left. Oh! I moved it. Is that free will? I dont think so. The whole thing - me wanting to move the right hand to the left, and then my moving it, and then writing this down, might have a perfect scientific explanation that explains it all. So even though, I feel that I have free will, even that feeling is just a deterministic result.
But this should not be depressing. Since who cares whether what we are actually doing is being determined by us or not? I can "feel" illusorily that I am doing what I want to. Thats it. This feeling of having free will, though false, is all that we need to feel responsible for our decisions. The actual reality should not matter.