The logic was simple. If we don't get them, the Russians will.
Operation Paperclip (originally Operation Overcast) started in 1945 and was a project in which the Joint Intelligence Objectives Agency (JIOA) actively recruited Nazi scientists, engineers, chemists, and doctors to come to America and do research for different areas of the government and military. Some of the scientists, doctors, etc. that performed heinous acts upon innocent people were sought out to help America with its research.
Before reading this I didn't know about Operation Paperclip. There have been other books about it and I would be interested in reading them. Quite frankly I was outraged at the behavior of certain Americans when they actively recruited these men and basically befriended them. I was outraged at the project but not surprised.
Annie Jacobsen spends a lot of the book discussing the research into who the important Nazi scientists, chemists, doctors, etc. were and the efforts by the Americans to track them down and recruit them to the project. She does also cover what those scientists, doctors, etc. did during the war and the work that they did for America after the war but I really wish that there would have been more of this in the book.
I would recommend this if you are interested in learning about Operation Paperclip.