While you're waiting for a direct answer to your specific question, I found a thread in which /u/mojohand2 specifically discusses the results of two polls specifically about William Calley and his punishment. Thread

Further searching turned up this thread, with a comprehensive conversation between /u/cadian16th, /u/ThoughtRiot1776, /u/flowartist, /u/eternalkerri and /u/Bernardito.

I'm extremely well read on the My Lai Massacre, but if I recall from my father who served in Vietnam, people felt sympathetic to the troops involved as they were following orders, regardless of the crime. Army Command had told them that all the people found in the area were either active Viet Cong or VC sympathizers. The sentence reduction for Lieutenant William Calley, the officer in charge of the US soldiers, was because many people saw him as a scapegoat; someone that the US Army could pin all the blame to. The fact was that it was a horrible mistake and in a war that was already unpopular as well as with morale plummeting, the US Army mostly wanted to try and downplay how bad the event was

https://www.history.com/topics/vietnam-war/my-lai-massacre-1