What's so bad about chamas?
Consequently, the person who was stealing considered it permissable and had no regrets for wrongdoing. And there's the rub,the feeling that one did nothing wrong when one has. That's what we see in the contrast between the first king of Israel, Shaul, and the next king who was chosen for the royal dynasty, David. When Shaul was chastized by Shmuel for having spared the sheep and Agag, he insisted he had not done wrong. In contrast, David didn't attempt to justify himself when Nathan told him he had sinned and immediately admitted that he was at fault.
My grandfather identifies that same kind of dynamic at work in the first sin recounted in last week's parsha. When G-d asks Adam if he ate of the forbidden tree, he responds, "haisha asher natata imadi hee nathna li min haetz vaochal." Bereishis Rabba reads the last word as the future tense, indicating not just "I have eaten," but "I will eat." That kind of defiance indicates no regret or even recognition of wrongdoing. And that is the real problem -- the failure to recorgnize one's sin, the first step toward teshuva.
I would add that we see this in addiction. The first step is for the addict to recognize that he has a problem. Only then can he resolve to fight his natural inclination to indulge his addiction. When one is in denial, though, and insists that he's fine just the way he is, he is bound to sink even lower. The same holds true with any moral failing, as well.
It was chamas even more than the other areas of immorality that sealed the fate for that generation because it represented that acceptance of breaking moral boundaries with impunity. "I'm not doing anything that I could be prosecuted for, and so I have done nothing wrong," With that kind of complacency, there is no hope for improvement.