I never said they wouldn't have gone Communist. I'm saying that the US under FDR might well have been more willing to work with Communist or Socialist governments instead of going fully them-vs-us. Insteasd of "ALL REDS BEING EVIL", maybe something more along the lines of "These are OUR Red, who do whatever the hell they want in their own countries but aren't a threat to international order, unlike the Soviets who are simply Russian Imperialists by another name."
Thus you'd be more likely to get a non-aligned Communist Vietnam willing to play well with the US. Sukarno, without seeing himself as being isolated and oppressed by all the Western powers, might well be willing to see the US as a counterbalance to the British and Dutch in the Indonesian War for Independence, rather than as IOTL, seeing them do nothing and as a result leaning further and further towards the USSR after Independence. In this scenario, you get a still socialist but more Nehruvian Sukarno. Nehru himself would be more willing to warm to a US with anti-Imperialist credentials.
This also allows the US to more effectively counterbalance the USSR in the Third World by disassociating itself from the Colonial powers, as opposed to being seen as their replacement.
The thing is Communism as being seen as evil happened much later than Truman. Truman and Eisenhower both tried to negotiate with Yugoslavia, hell Yugoslavia was considered to be a part of wedge strategy to divide the Second World very early on. The thing is even excluding, the fact the Yugoslavs shot down a U.S plane, the Yugoslavs were seen as too unreliable to be allies. Only the fall of China and to some extent the Korean War made opposing Communism seem to be the only viable option, both can't really be blamed on Truman.
The U.S tried the same with China under Mao for a little bit too, and Mao had reasons to be pissed at Stalin, not really helping them in the Civil War,even after the Maoists won, Stalin made then sign a trade deal that greatly favored the Soviets, and still was pissed off he had to wait during Stalin's birthday to do so. This last part I don't know if this ever made its way into Mao's judgment, but Stalin backed Sheng Shicai the card carrying communist warlord of Xinjiang, who then defected back to the KMT and had Mao's younger brother Mao Zemin killed as well. Mao went with the lean to one side approach, anyway.
So it's not like the U.S was locked in Communism=Evil, at least not abroad. Hell, even the Domino Theory changed with times to point of going from we need to intervene in Vietnam to prevent the spread of Communism, to we need to stay in Vietnam to prevent the much more dangerous Chinese from gaining influence and causing war. Basically, long story short The U.S tried to take a pragmatic approach, but regardless other nations didn't bite.
Don't leave out the Chinese, 3-way competition took place as well, with Maoism and it's National Liberation being an alternative to the Soviets and the U.S.