Ask Lemmygrad

If I was a Marxist-Leninist Maoist, and said anything as an answer, in my prediction, it would be that

"sure, Mao did support the Khmer Rouge, during the Vietnam War (understandably, due to the U.S make their forced error of bombing Cambodia), but Deng was the one who continued it to the end, even as the Khmer Rouge turned anti-communist!"

and then some ML-Maoist anti-Deng dribble of Deng's foreign policy reflecting that of their market reforms and revisionism...

I hope I'm proven wrong, of this matter, cuz otherwise,

I've never seen them able to justify it, they usually don't understand the history behind the Khmer Rouge and the Vietnam war. Vietnam was literally the only just actor in the whole history of those conflicts.

I've seen self described Maoists just be pro-Khmer Rouge and you could tie this with the fetishization of violence in the movement because it's often not a critical support either that takes into account their awful situation but just saying the genocide was deserved and shit (often playing into anti-communist exaggerations of the already horrible events too). Western Maoists are a different breed tho than the CPI (Maoist) so I'm not sure about the latter's thoughts on the matter or any of the other third world Maoist parties.

Some Hoxhaist anti-revisionists that don't take the whole Maoist line also cite Hoxha's "Can the Chinese revolution be considered a proletariat revolution?" to discount the project as communist/marxist and paint it as revisionist from the beginning, laying this to blame for their tactical moves with the US

Wasn't the falling out with Vietnam essentially a side effect of Sino-Soviet split? Mao wanted Vietnam as China's satellite while Vietnam wanted independence and wouldn't cut ties with the USSR.

I don't have the expertise to answer this, but it's a question I've had in my mind for a long time.