Much has been made about the philosophical implications of determinism. Generally it is seen as opposed to free will, but this, to my mind, is a mistaken dichotomy.
Consider this situation. A man has been arrested after being caught brutally torturing and murdering people. Further analysis reveals that a serious chemical imbalance in his brain has caused him to be delusional and violent. Maybe it's even possible to treat the chemical imbalance, and thus reform him. Another man is arrested for similar crimes, but no physical cause is detected, and thus, no cure is offered other than long social retraining with a low chance of success.
Most people would be inclined to forgive the first person by saying that his actions are "not his fault". The moving about of chunks of blame is very important to people in a situation like this. But the latter person should not be forgiven, since it's his own choices, and people should take responsibility for their own choices.
Ultimately, though, anyone who is moderately well-educated about things like psychology, the body-mind connection, and the history of our understanding of neurochemistry, has to realize that odds are very good that the second person also has something physical going on which we simply don't know how to diagnose and treat yet. A hundred years ago, these two men would have seemed identical as villains; and a hundred years from now they may again seem identical as victims. But today, they seem as different as night and day.
The principle of determinism takes this conundrum much farther. The idea is that a full knowledge of and understanding of the state of all matter and energy in the universe would, given sufficient time to compute, allow the prediction of all future events, since those events are determined by physical interactions of matter and energy, not by whimsical transcendant spirits. (The fact that it would take a few thousand universes to store the information to describe our one universe is immaterial. The point is that in principle it could be predicted and therefore is determined. The only randomness left is that we don't know what will happen, but what will happen is still determined by what is.)
So if everything you're going to do depends on physical characteristics, ranging from the state of a wave of light passing through space near you, to the chemistry you got from your parents, to the intricate and unseeable clockwork of electrical forces in your brain, then does that mean you are not responsible for any of your actions? Everything is determined ahead of time. We are only playing out a script written in the first moments of the universe. So who cares if you take that last donut? You were always going to.
But this doesn't make sense to me. If you did something bad just now, it doesn't matter if you did it because of something that happened earlier. Causes are not exclusive. Every cause in turn has a cause, but that does not take away the significance of the proximate cause. (This fallacy, the assumption that one cause obviates another, is one of the bigger ones in spurious logic.)
If you accept that it makes sense to judge people and their actions at all, then it seems clear that you can do so equally well in the case of both murderers. Both murderers did the things they did, because they were, at the time, the kind of people who did those sorts of things. There are reasons why they were those kinds of people, but that doesn't change that they were.
So what's really different? In one case, we can change what kind of person he is. That change does not change the past; it does not change what he did, or the fact that he was the person who could do those things. It doesn't obviate him of responsibility for his past. But it does change who he is now; and therefore, it changes how we feel about him. We can certainly deplore who he used to be and accept who he is now, if we're emotionally strong enough to accept the change (and if the change really is as good as I'm presuming). In the other case we can't make that change happen.
But in all these cases we can still judge someone based on who they are and what they do at any point in time, and the particular causes for why they are and do those things don't really enter into the judgment. It's no better or worse to be a killer for one reason than another, as long as in both cases, you're a killer.
Furthermore, and perhaps ironically, while nowadays people are inclined to imagine determinism and free will are opposed, a more historical viewpoint will reveal that the realization of determinism was actually a liberating concept. Before determinism took sway, people tended to imagine that the world around them, from the small to the large, was controlled in large part by the whims of gods and spirits who could not be understood, and only sometimes even appeased. In a real sense one's fate was out of one's hands. Determinism tells me that I can come to understand the actual causes of events, measure them, and manipulate them, without them depending on a whim completely outside my sphere of influence or even understanding. Determinism means my actions have a large part in determining my future.
Nowadays people look at determinism and can only look backwards and fret about the implication that determinism causes your actions, but it's just as important to look forward and see how determinism allows your actions to cause your future, too. It's a sword that cuts both ways. If you are a brilliant mathematician, do you say it means nothing because your father had a particular allele, or because a teacher you had in fourth grade motivated you? No, you can still be proud to be the person who is the accumulation of all those causes, who is thereby a brilliant mathematician. Determinism does not take away anything from your pride, your responsibility, your celebrations, your remorse, your accomplishments, your mistakes. They're still yours. In fact, determinism is what makes them yours.