There's a number of questions that were raised in this work that the author mentions, and I'll list them here:
- What was the rationale for picking targets? - Why does it appear that U.S. planners went for such amazing overkill?
The year provides a clue, and an important context: In the 50s, the strategy was "Massive Retaliation". WWII ended 11 years prior. The Soviets had a massive army in Eastern Europe, and the Korean War had ended only 3 years earlier, confirming many people's fears that the Soviets were willing to implement Communism by force. Given that the Western Powers had no hope of conventionally halting a Soviet attack on Europe, the plan called for an immediate escalation to nuclear weapons; which were the only credible threat to Soviet ground forces at that time.
The other important context is that while this is a full target list, it isn't a /plan/. And that was because there wasn't a plan yet. Air Force targets overlapped Navy ones, and early doctrine called for simply attacking everything should hostilities begin. This was changed in 1961 with the Single Integrated Operations Plan, which for the first time was a single plan with no only a target list, but different escalation options, assignments to various services for who struck what and when, and a much clearer rationale. It was a vast improvement over the "simply hit everything vital" days of Massive Retalitation.
On the subject of overkill, it's also useful to point out that it was not expected that all warheads would reach their targets. the ICBM was in it's infancy, and SLBMs (submarine launched) did not yet exist. The B-52 had only just entered service; the mainstay of SAC rode on the B-47. Nuclear Weapons were large, sometimes unreliable, unwieldy things. In many ways, the target list was wishful thinking.
Some good reading: If you read only one, read this: https://en.wikipedia.org/wiki/Single_Integrated_Operational_...