Moral Relativism, also known as Situational Ethics, is what has caused the decline of the Liberal Left. It began with the with the idea that "Nothing is always right or always wrong." Ironically, this is an idea that they feel is always right. It is, however, an idea that is easily proved wrong. For example, it's always wrong to oppress people, or to commit genocide.
Moral Relativity has been combined with several other ideas to create what we think of as the modern liberal. Here is the way it went:
In the nineteen-sixties the idea that we should tolerate each others differences (at that time primarily racial differences) was pushed hard in schools and the media. This was, and is, a noble idea. It was referred to as "Racial Tolerance."
Racial Tolerance gradually became simply "Tolerance," and began to include under it's umbrella tolerance for other cultures, nationalities, religions and forms of sexuality. Still a laudable concept. Our Declaration of Independence begins with it, "We hold these truths to be self-evident, that all men are created equal."
The idea of "Tolerance" began to meld with the idea that "Nothing is always right or always wrong" and became "Nothing of ours is better than something of theirs" and then more recently mutated into "Nothing of ours is ever as good as anything of theirs."
This can be seen today in the fact that the Left is only upset by the use of force when it is the U.S. using force. In the fact that, if the U.S. has a vested interest in the use of force, it is unacceptable to the Left, but if there is no benefit to the U.S. at all the use of force is mandatory. Take, for example the difference in the Left's resistance to the use military force in Iraq (How dare you?) and their desire for the use of force in Liberia (How dare you not?). In Iraq we have many vested interests, in Liberia none.
It can also be seen in the drive to multi-nationalism and the desire to subjugate the will of the U.S. to the will of the United Nations. They believe that only other nations could be fair and impartial enough to decide whether the U.S. is threatened enough to require the use of force to protect itself. They believe that only other nations could be fair and impartial enough to try Saddam Hussein for his crimes against the Iraqis. The U.S. is, in their eyes, incapable of the exercise of power or judgment in any way other than bullying self-interest.
It can be seen in the Left's approach to Abortion. Does this sound familiar: "I don't believe in it myself, I think it's horrible, but who am I to tell other people what to think?" They can't see that there is an absolute involved; that Killing is bad, and should only be done to protect yourself and others from people who will not be dissuaded in any other way.
They also believe that the Government is better suited to taking care of us than we are ourselves. In this case the Government is the "other" who's "everything" is better than our own.
Our culture is not as good as Europe's, our leaders are not as smart as the United Nations, our medical system is not as good as Canada's. Our fill-in-the-blank is not as good as their fill-in-the-blank. In an all-out war they believe that the enemy has a greater right to defend themselves than we do. What it comes down to is that they don't believe our culture/country/lives are worth fighting for because they aren't worth a damn. Because nothing of ours is ever as good as anything of theirs.