The whole thing is really a great read, here's a snippet:
Why do things get worse so fast? Of course we have names for the process, like "collapse," "decay," and "slippery slope." By conjuring images-a stricken house, a gangrenous limb, a sliding talus-they make us feel we understand. Now, I am no enemy to word-pictures, but a civilization is not really a house, a limb, or a heap of rocks; it cannot literally fall in, rot, or skid out from underfoot. Images can only illustrate an explanation; they cannot substitute for one. So why do things get worse so fast? It would be well to know, in case the process can be arrested.
The usual explanation is that conscience is weakened by neglect. Once a wrong is done, the next wrong comes more easily. On this view conscience is mainly a restraint, a resistance, a passive barrier. It doesn’t so much drive us on as hold us back, and when persistently attacked, the restraining wall gets thinner and thinner and finally disappears. Often this explanation is combined with another: that conscience comes from culture, that it is built up in us from outside. In this view the heart is malleable. We don’t clearly know what is right and wrong, and when our teachers change the lessons, our consciences change their contents. What once we deemed wrong, we deem right; what once we deemed right, we deem wrong.
There is something to these explanations, but neither can account for the sheer dynamism of wickedness-for the fact that we aren’t gently wafted into the abyss but violently propel ourselves into it. Nor, as I will show, can either one account for the peculiar quality of our present moral confusion.
I suggest a different explanation. Conscience is not a passive barrier but an active force; though it can hold us back, it can also drive us on. Moreover, conscience comes not from without but from within: though culture can trim the fringes, the core cannot be changed. The reason things get worse so fast must somehow lie not in the weakness of conscience but in its strength, not in its shapelessness but in its shape.