I think this entire topic IS rather over done but that doesn't mean that it has ever been done well, and this happens to be a topic that I like so I'll just pipe up as though invited and say my two bits. A fairly recent neuroscience experiment demonstrated that by the time a conscious decision is registered in the mind to perform an action the motor cortex has already started sending the signals to the body to do it. So NO, we don't have the 'free will' that we think we do, what we have is a half baked combination of limited freedom and one hundred million knee jerk reflexes. But instead of jerking the knee, you jerk something else. Anyway yes you can pretend that you have free will and go around making choices and that's all well and good but the bottom line is this. You can entertain the idea of doing anything, but you will not actually do anything, you will actually only do one of a few things, and you will magically decide to do so just a special moment after you already started doing it, cellularly speaking. Imagine you're a passenger on a boat at...disneyland. And you're riding along and turning the wheel and wearing beautiful mouse ears and you are totally convinced that you are driving, but in fact, you aren't. And you're five. And your parents told you that you're driving.
I think I just explained it badly but in answer to the original question yes and no. You would be able to predict what a person could do, but again it's like a rail shooter, you could shoot the criminal on the left, or the right, but you WON'T turn around suddenly and jump out of the car.
"But what about people who kill themselves" Well I hope I'm not alone in thinking that people who commit suicide have something wrong with them. I think that's thoroughly addressed now.
I like to think of the human mind as a gigantic pile of instincts all talking to each other about one or two things. And sitting on top of the pile is the person, whatever that is, who points and can shout and develop opinions but only insofar as the rest of the pile lets him.
And yes, you can get your brain to let you do things that it doesn't want to do. Try a little experiment at home. Ask a friend to walk five paces up to you and punch you in the face as hard as he can. Not the gut, or the chest, the face. You will flinch almost every time, and if you don't you'll probably hit him back. (actually don't do that at home, it's not safe but you get the point). You'd have to try a number of times to actually let someone hit you, certain martial arts schools make this part of the training, where you practice getting hit so that you can take it in real life, and this is because when the brain sees someone coming to hit it it doesn't want to get hit, which is smart, but then there's a five year old sitting on top of it saying "yayy, yayy, come hit me" and it'll take a while for it to listen, if it ever does.
I've over simplified things here a bit. And I just watched about twenty ZPs back to back.
Anyway, Hello World, it's me, 300ccs of medicine, nice to meet you.