MORAL REALISM AND DEONTOLOGY:
"The motto of the deontologist is "let justice be done, though the heavens may fall.""
"If popular views are resistant (as they are) to utilitarianism, there may be something to learn from that and not merely something to explain about it."
-Michael Walzer, "Political Action: The Problem of Dirty Hands"
Deontology (at least the species of it that I follow) can look an awful lot like rule-utilitarianism, so I'm going to attempt to shortly explain why I personally can't accept utilitarianism as a moral system, and why I think deontological thinking is much more appropriate for governmental and personal life.
The reason I can't be a utilitarian is, essentially, because I'm a moral realist: I think that right and wrong are concepts that attach themselves to actions in meaningful ways, and further that it's entirely possible that a person can not know what the right action is at any given moment, or decide not to do it because of bad logic or any other reason you like. The failure of people to do the good (or even to recognize the good) has nothing to do with what is the good. So the utilitarian ethic has to be rejected because there will be at least some cases in which what a person will decide benefits them most is not what is actually good for them (of which there are numerous examples in moral philosophy, pick the one you like).
Deontology sort of builds on this concept by saying that an action that's morally wrong is always morally wrong, no matter what the context or outcome: if it's wrong to kill someone, it's just as wrong to kill a child as it is to kill Osama bin Laden.
The general criticism of deontology is that this is an overly harsh way of approaching things: it's not at all the same type of act to kill the two above-listed people, even if the same action is happening.
This isn't, I think, what deontology on balance wants to say: it merely wants to assert that utility-following is going to lead you down the wrong path sometimes, and also that the moral elements of a complex action don't get washed away because the action is complex. To use the example floating around the blogosphere at the moment: suppose there's the ticking time bomb and the known terrorist who's in on the plot who's the only one who knows where the bomb is. Should you torture him to get the information?
Yes, the utilitarian will say, because whatever you lose you gain (and more) by preventing the bomb from going off. Right to do so. End of story.
Yes, the deontologist will say, because you've got two (at least) competing moral claims, but your obligations as someone with the welfare of others on your head outweighs (in this case) your obligations to your own conscience. So do it. But you should feel perfectly awful for doing so, because you just broke one of the big moral no-nos.
Why does deontology make for a better politics? It encourages two trends which are helpful:
1. An ethic that's built around the idea of positive obligations you have towards other people (which is important, since we know there are some people who are radically corrosive of moral norms, and it's in everyone's interest that they be stopped).
2. That moral rules are not to be taken lightly--they aren't determined by the circumstances (only the actions are), and that the moral status of actions is something that should be front and center whenever a political actor is making decisions.