They placed an awful lot of faith in the work of Michael Caldwell - who was a Khmer Rouge apologist right till he died. Quite possibly at the hands of the Khmer Rouge.
Going a little bit off-topic here, but it's kind of my hobby ...
From Caldwell's private notes given to Ben Kiernan (who was also denounced as pro-Pol Pot for his earlier involvement in an academic bulletin from Australia's Monash University named News from Kampuchea in the mid-1970s), it appears that while having sympathies he was fairly sceptical while on his visit to DK in December 1978, along with Richard Dudman and Elizabeth Becker.
He was most likely murdered by a RAK soldier/s, two days before the Vietnamese invasion. His positive work on DK (Cambodia: Rationale for a Rural Policy) was published posthumously. I've never read it though, so not sure if it's in a similar vein to Cambodia: Starvation and Revolution by Gareth Porter and George C. Hildebrand.
To be fair to the SWP (not something I say very often!) they weren't the only ones to have an initially mistaken view of the Khemer Rouge. Chomsky's writings at the time certainly raised my eyebrows when I read them.
It's understandable people on the left may have been skeptical when the first atrocity stories started to filter out. Western news reporting on South East Asia had been a model of lies, spin and propaganda against anti-imperial movements since the insurgency in Malaya in the 50's.
Plenty of others were suckered in, people of various political stripes who were a part of the western anti-war movement wanting the US out of ex-Indochina, but also members of small, western China-oriented parties. The Chinese were behind encouragement of the CPK to go public as a Marxist-Leninist party and government in 1977, and as a new war with Vietnam was looming, by 1978 there was a drive by DK to open up more and make better ties with the outside world, in order to gather support in the event of a new conflict. It will have been through fraternal relations that these tiny sects had with the CPC that saw invitations given out to go on Potemkin tours of DK.
One such sect was the Communist Party USA (Marxist-Leninist), which followed the CPC line at the time, with the Mao-Deng Three Worlds Theory and the Soviet Union being the main danger, the imperialist power on the rise etc. After the full horror of Pol Pot's regime became undeniable, the experience of finding out they'd been fed bullshit led to its young, middle class and idealistic members left hopeful by the Communist victories in 1975 becoming disillusioned and resigning, pretty much causing the collapse of the organisation. One of them (Daniel Burstein) is now a venture capitalist. Another former member (Carl Davidson) contacted me by email a couple of years ago after I reproduced the party's English translation of Pol Pot's crap, crudely Stalinist CPK congress speech from 1977 (when the existence of the Communist Party was revealed to the Cambodian people and the outside world):
Yes, it is the same Dan Burstein. And the correct name of our group then was simply Communist Party Marxist Leninist (CPML). When Burstein and the small group that visited Cambodia later discovered they had been mislead and lied to on their tour, it caused a crisis for them personally, and for our organization as well. Dan resigned his post, saying he was no longer a Marxist-Leninist--he was in his mid-20s at the time--and retreated into private life. Later he wrote books on Japanese economics and China for the business press, as well as other nonfiction works, and became a small-time venture capitalist. Dan's resignation started a process of liquidation within our group, and within a year, we were defunct.
I was editor of Class Struggle, our theoretical journal, and I made the decision to print Pol Pot's speech as an appendix in one of our last issues. I recall thinking that his politics were rather strange--calls for abolishing money, setting up communism immediately, etc--but since his thinking wasn't available anywhere else in English for people to study, I made it available, since he was the leader of a party that had taken power vs. the US imperialists.
I've mentioned this a few times to younger comrades and activists, to warn they [sic] against dogmatism and flunkeyism--and to take anything coming from any party regarding its achievements with a grain of salt.
Their booklet of the tour. Oh dear.
Earlier than that though, naivety and misunderstanding about Communist politics and how they played out during the wars was present. This ignorant student poster from the University of California, Berkeley, made an appearance back in 1975, but by the time of the Communist victories (two weeks apart) some of the CPK leadership (Pol Pot and friends) considered the Vietnamese to be irreconcilable enemies of their revolution.
The person/s who made this poster weren't up to speed with the troubled relations between the Cambodian and Vietnamese parties, perhaps relying on wartime information provided by Hanoi and the Chinese Communist press, emphasising solidarity between the national liberation forces, including glossy, English-language publications promoting the National United Front of Kampuchea (the French acronym being the slightly amusing FUNK).
Also, the poster uses the name Khmer Rouge to describe the Cambodians. CPK members didn't refer to themselves as such, it being a pejorative epithet used by Prince Norodom Sihanouk to inaccurately label his (intellectual and publicly active) leftist political opponents during the 1960s. Not all the people labelled as ‘Khmer Rouge’ were a part of the underground Communist movement at that time. The name stuck, however, to describe the Communists generally, this being in part due to its use by western journalists.
I think quite a lot of people will be feeling silly and ashamed in their old age.
That's it, I've bored you enough. I'm gone.