This newer research by Bart Hendrickx sheds a new light on the decision. [1] [2] The actual decision to build it was made by engineers, not the party or the paranoid military, and was based on wrong assumptions, like the US military requirements that were already known to be dropped, not making it into the final Shuttle design.

[1] https://www.thespacereview.com/article/3873/1

[2] https://www.thespacereview.com/article/3876/1