Just think of how Patton and MacArthur were right and that would have saved so much bloodshed/problems we have nowadays if we had gone after the two evil regimes at that moment in time.
I used to think the same thing. The standard teaching is that the US was very war weary, and after the war ended, the people would not have accepted several more years of war to defeat the Soviets. Not being alive back then, I can't judge the mood of the people, but it is also possible that the Communists who had the ear of the President influenced the decision-making, and then wrote the textbooks. Looking at it from today's vantage point, holding nukes and an Army in Central Europe, it would seem to have been quite doable--if we were willing to use the nukes. Another aspect of it is the US people were given so much pro-Soviet propaganda during the war that they needed some time to start viewing them as the enemy. People in general didn't think of the Soviets as our enemy until around 1947 or 1948.
After we won the cold war, I was more ambivalent about it. We won by playing it safe, so it all worked out, and maybe it would not have if we had gone to war with the Soviets early on. But maybe, just because we got lucky and it worked out, it was still wrong to risk defeat and have all those lives lost to communism, just to avoid a direct confrontation.
The most powerful man in the history of the world was Harry Truman, but he sat on his power after August 1945, and by 1949, he was no longer so powerful. What's done is done.