The reason MacArthur is vilified by Marxists/Progressives is because he was a conservative/Republican general and a out spoken one at that. After the Chinese entered Korea things did not go well for MacArthur. Several creatable historians strongly suspect that after Inchon Chinese/Russian infiltrated the command structure in DC and were privy to his strategic plans. They point to the fact that when things were happening to fast for the chain of command to operate MacArthur's battle plans did quite well.
It is also worth noting that after Truman fires MacArthur the USA never really won another war/occupation. MacArthur fought to win, he fought Washington as hard as he fought the enemy in Korea, so he was fired and hence forth US commanders were gelled and silenced.
Arguably, some of those operators in place may have been left over from FDR's days. You may be aware that several years ago there was quite a discussion about John Kerry's father, who worked at the State Dept during that era, and his political inclinations. Growing up at the Kerry dining room table probably accounts for Sen Kerry's world view.