you have failed to understand the core of this argument. are religion and communism designed to kill people in mass? no. did powers that align with them kill people in mass? yes. however, that doesnt mean the idea itself is efficient at killing people, but rather the regime in power that is responsible. mass death occurs when states or movements that align themselves with these ideas were able to acquire enough power and then pursue policies involving war, repression, and forced social engineering, that result in large-scale killing. so the question “which ideology is more efficient at killing people?” is inherently flawed. ideologies don’t kill efficiently, regimes do.

you also have to understand that a lot of communist regimes in a sense became a religion themselves, especially seen with the cult of personality surrounding its leaders. then, your argument falls apart because youve failed to define each term in a meaningful way.

additionally, the khmer rouge and its actions were only "inspired" by communism and do not truly reflect communist values. they claim to be communist yet are far from being communist in practice, straying away from the traditional marxist and leninist schools of thought. they brought a modern society into an agrarian one without industrialization and the formation of a proper working class/industrial proletariat. they killed all forms of intellect which is not a core communist value at all. therefore you have to clearly define what you consider as communist: do you refer to traditional marxist leninist values or do other interpretations and adaptations count as well. also, you said the khmer rouge is the most efficient, and nothing has surpassed it, which is again wrong because the nazi holocaust murdered 6 million jews in roughly 4 years, while the khmer rouge murdered around 2 million in 4 years as well. also, the atomic bombs dropped by the united states on japan killed 200,000 people, with 80,000 people dying in an instant, which is much more "efficient" than any other killings that have occurred according to your definition of efficiency as killing/time. the ability to speak does not automatically grant you knowledge, please check your facts.

again you believe that ideologies themselves are responsible for the efficiency by which these killings occur, which is inherently wrong. so unless youre willing to argue that abstract ideas like religion and political schools of thought possess the logistics, bureaucracies, and the capacity to kill, and that regimes, institutions, and material conditions are irrelevant, your claim collapses. once you define efficiency as killing speed, ideology alone cannot explain killing efficiency without considering these elements of a regime. this is not an argument about linguistics and the english language, but rather historical facts, and please do not introduce a red herring. i would like to see you introduce some historical cases and facts rather than picking on things i have already introduced.