Why did the US appease Communism?

Indeed, I have no real answer to this question, except that the president of the US never anticipated that the Soviet Union would survive the Second World War.

Why I am going back to this old shoe and re-examine it once more?

Well, one thing is this report from Der Spiegel. The other is the way people defend the US president today for his unrelenting view on attacking Iraq and how they compare it to the resolve of the US during World War II. They say that the president is persuing the goal of freedom and liberty as the US did during the Second World War and that there will be the same effect as then.
I don't think so. It might be, that it works, but only if the president would really believe in liberty and peace, which he does not. His constant appeasement of religious leaders in Iraq have shown his weak side as much as the still nationalized oil wells. Both issues are signs of limited resolve, but it is increasingly like and unlike WW II.
It is unlike WW II that it has not the necessary philosophic grounds to apply a liberal democracy and a unified country, like Germany and Japan. Instead, Iraq is rooted into three different social tribes (Kurds, Shiites and Sunnits) and it has a philosophic background that concludes in a theocratic authoritarian dictatorship.
So, the formal aspects are clearly different compared to World War II.

So, perhaps the personal and ideologic aspects of the "liberator" are perhaps comparable? Yes, they are, but only on those aspects that led to the 40 year reign of the Soviet Union.
For example, and I think this is the strongest evidence, we have the resolve of the US president to form a democratic Iraq and destroy any remaining "Terrorist"-threat. Since the threat is rooted in radical Islamism, he has to prevent this theology to become dominant in Iraq. He has failed in this.
Now, the comparison to World War II shows that the Allied Forces also failed in this. They bargained with evil (or better Stalin) about West-Berlin and lost most of the later DDR territory to the UdsSR. They had already seized Leipzig and other cities in Eastern Germany, but instead of driving further against the threat of socialism. They stopped and returned the truly liberated territory to the Soviets.

The same thing happens in Iraq, instead of solidifying a liberal position in Iraq, president Bush has appeased the Islamic forces in Iraq (Shiites mostly).

So, let's not draw yourself into the false aspects of the comparison between the Iraq situation and WW II. The aspects that led to a success in Germany are utterly different from Iraq and the aspects that compromised the probability of a maximum victory, are the only ones one can compare.