First, I want to suggest that there are three broad "tiers" of moral judgment; an act can be:
Is lying an objectively immoral act? The Biblical God explicitly forbids it in the 10 Commandments, and most of us believe, in general, that lying is wrong. But it doesn't take much effort to imagine a circumstance in which lying is either permissible or even morally obligatory –unambiguously the right course of action.
In Nazi-occupied Poland, families sympathetic to the plight of Jews would hide Jewish families in the attics, walls, or basements of their houses. When Nazi officers came around inquiring as to the whereabouts of these Jews, the families lied to protect them.
Most reasonable people would agree that in this circumstance, it was not merely permissible to lie – lying was the morally obligatory course of action. If this is true, it means that the act of lying cannot be intrinsically, objectively wrong; rather, we make subjective value judgments as to the "rightness" of the action depending on the circumstance. If lying were objectively wrong, it would always be wrong.
It's easy to imagine this with virtually any other act. Is it moral to indiscriminately kill civilians en masse in a time of war? We've evolved our weapons of warfare to minimize civilian casualties – we use laser-guided bombs and missiles, precise rifles fired by trained marksmen, etc. If we had no care of killing the innocent, we could simply drop as many nukes as it took to wipe our enemies off the face of the earth.
But in World War II, the United States dropped two nuclear bombs on Japan. In those two explosions, hundreds of thousands of people died – most of them civilians. And the ones that were evaporated were the lucky ones – many more suffered slow, excruciatingly painful deaths from radiation poisoning. But in this case, the US military had made a subjective value judgment – that the show of force of the atomic bombs would force Japan to surrender, ending a war that, if protracted, would likely escalated to a full-scale invasion of Japan and cost millions more lives.
Regardless of whether one agrees that this action was either wrong, permissible, or obligatory, the fact remains that it was an act of genocide that was circumstantially justified through subjective value judgments. As horrible as we generally think genocide is, even genocide is not objectively wrong. If it were as simple as saying something like "lying is objectively wrong", then we would quickly run into an impasse as various objective moral tenets conflicted with each other. The Nazi example is a fine one; is it not also wrong to passively allow the abuse and murder of other humans when it is within our power to prevent it? While surrendering our power to help others is an act of omission, and lying is an act of commission, I think most reasonable people would agree that in this case, the act of surrender would be the greater moral crime, and lying was the right thing to do.
All moral actions require subjective judgments which take into account external factors that influence whether an act is forbidden, permissible, or obligatory. No act exists in a vacuum where it can be considered absolutely and objectively right or wrong. Only one issue remains: how do we determine, then, what constitutes right and wrong? As I've already suggested, though our judgments are necessarily subjective, our reasoning is not arbitrary. I'll be doing a third post on morality soon (hopefully this weekend), and the nature of moral reasoning will be its subject.