Firstly, the KR was willing to exterminate an entire people, and sacrifice a quarter of its own population to do so. Secondly, the KR had little regard for the lives of its own ethnic group: Khmers were expendable. Thirdly, the disjunction between means and ends would be comical if it were not so tragic. The Vietnamese had just defeated the USA, yet the KR was planning a total war against them.
Kiernan's estimated death tolls from the domestic genocide can be found in Figure 1 here. The KR divided the population into the 'New' and the 'Base'. The 'New' were those who had lived in government-controlled territories in the Lon Nol period (1970-75). The 'Base' were those who lived under the KR insurgency during those years. The 'New' were given the lowest status and fewest rights, and were subjected to brutal deportations across Cambodian zones. These were ostensibly for forced labour, but, as Kiernan shows, they made little economic sense. There was at least one occasion where a large group was forced to plant the harvest in one area, but was then moved to the North West, where there was insufficient food, rather than being fed by the harvest they had sown. These groups died by shooting, starvation and disease in roughly equal numbers.
It is not easy to fit their deaths into conventional genocidal categories. They belonged to the same ethnic group as the regime. However, the KR ideologies used to justify their deaths may be defined, in part, as 'pollution' concepts, which I discuss here. In Japan, the ethnic group the Burakumin:
bear the name "Eta", whose literal meaning is "full of filth", "full of pollution" or "abundant defilement" (Lifton, p.482).The 'New' were subjected to this same terminology, and were thus placed in a caste-like status which made them socially dead and therefore expendable.
The Khmer Rouge's killings were also motivated by paranoid nihilism. It was a state whose central aim was to destroy other systems, cultures and physical beings. Although the Khmer Rouge had dreams of building a utopia, the process of destruction was its motor and thus eventually became its ends. The means became the goals.
In conclusion, therefore, the question of whether the KR was Maoist, or an economic deformation of Maoism, is largely moot. Maoism was merely the vehicle to which the KR hitched its paranoid, genocidal nationalism. Death through forced labour, justified by trite Maoist language, was simply one of the means used to perpetrate a genocide that had its roots in the ultra-nationalism of its leaders, driven to pathological extremes by racism, 'pollution phobia' and paranoia.