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.
How about saying that international relations aren't much to do with economic ideology, and are more about realpolitik
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.
Yes, but China took it way too far. China sided with the USA and armed the Khmer Rouge and continued to support them even after the Vietnamese kicked the KR out of power exposed their crimes to the world. They invaded Vietnam as punishment and got their asses handed to them. China and the USA continued to argue that the KR hold its UN seat despite not holding power and massive crimes.
Jup, didn't help tho that Vietnam escalated border tensions and insisted on upholding the claims of the former south Vietnam regarding the south china sea.
Mao flatout wanted not to have China encircled by soviet aligned states. Neutral was completely fine. The DPRK, for example, went neutral during that time, Juche becoming the offical ideology around that time, it evaded most of the bullshit that came out of the split.
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
I don't have the expertise to answer this, but it's a question I've had in my mind for a long time.
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 he died before he heard the worst of its massacres, and Deng was the one who continued it to the end, even as the Khmer Rouge turned anti-communist and attacked Vietnam!"
and then some ML-Maoist anti-Deng drivel of Deng's foreign policy reflecting that of their market reforms
