Final answer:
Bill Erhardt may have stopped thinking about the propriety of the Vietnam War due to changing public opinion, the credibility gap between the government's reports and the truth, and the brutalities committed by U.S. soldiers.
Step-by-step explanation:
Bill Erhardt's lack of consideration for the propriety of the Vietnam War once things became chaotic can be attributed to the changing public opinion, divide within the nation, and the brutalities committed by the U.S. soldiers in Vietnam.
The Vietnam War was widely protested and criticized, leading to a credibility gap between the government's reports and the truth revealed by leaked documents such as the Pentagon Papers.
The My Lai massacre and other incidents further eroded public support for the war. Therefore, Erhardt may have stopped thinking about questions of the war's propriety due to the overwhelming evidence against it and the disillusionment caused by the actions of U.S. soldiers.