Atheism, defined as the lack of belief in gods, isn’t an -ism, isn’t a worldview with dogmatic tenets…or any tenets at all. It’s a position on a single question.
While not your main point, I’ll still note that that’s not a satisfactory definition, because, for one, it’s not narrow enough, as the apparent genus is incorrectly identified. A dog lacks a belief in theism, but a sane man would never call any given dog an atheist. On the other hand, I doubt you meant “lack” in the proper sense in order to specify only rational agents capable of forming beliefs, since that would indicate privation of a due belief and you likely don’t ever find anyone to be at all lacking in that particular area.
How would atheism be “a position on a single question” if it were simply a
lack of something (namely belief) and not instead
a proposition or theory of one assertoric variety or another? Atheism, presumably that abstract sort of thing to which atheists affirmatively assent their minds, is fundamentally some claim to truth. In other words, at the end of the day, under its intuitive, common usage, atheism is either true or false; it’s not a mere personal descriptor, not just some character trait to be determined by one’s possession or non-possession of a potential belief. Here’s the right definition:
atheism is the assertion that there do not exist any deities; or
atheism is the assertion that theism is false.
Meanwhile
theism is the assertion that at least one deity exists; or
theism is the assertion that God (as conceived in Judaism, Christianity, Islam) exists.
Thus theism and atheism are two mutually inconsistent, contradictory propositions that may be assigned their own respective truth-values based on an objective fact about the reality in question.
Secularism, however, can arguably be considered a worldview or a system of organizing society. As such, it’s conceivable that someone could kill “in the name of secularism,” but in the case of the secularism we now see in the West, which is intertwined with humanism, a worldview that repudiates genocide and puts a great deal of value on human life, it would be almost impossible for anyone to kill in the name of that form of secularism (and still be logically consistent).
Replace ‘secularism’ with ‘religion’/‘Christianity’ and ‘humanism’ with ‘Catholicism’.
Christianity, however, can arguably be considered a worldview or a system of organizing society. As such, it’s conceivable that someone could kill “in the name of Christianity,” but in the case of the Christianity we now see in the West, which is intertwined with Catholicism, a worldview that repudiates genocide and puts a great deal of value on human life, it would be almost impossible for anyone to kill in the name of
that form of Christianity (and still be logically consistent).
Unless you’re simply attempting to exonerate humanist secularism while likewise maintaining the innocence of Catholic Christianity (which may of course be the case), you’ve either proved too much or too little here.
Hitler killed in the name of a nutty racist philosophy, and Stalin killed in the name of a nutty Communist ideology. Both of those nutty positions are consistent with atheism and arguably consistent with some form of secularism, but the atrocities that resulted from those positions cannot be argued to be caused by atheism or secularism (and certainly not caused by the humanist secularism currently practiced in Western countries).
Like I mentioned before, according to Lenin himself, to name only one, Marxist revolution
demanded atheism, anti-clericalism, and secularism in theory and in historical practice. There does seem to be a correlation between the theoretical atheism of Marx, Lenin, et al., and the documented tyranny of Marxist-Leninist revolutions. If a revolutionary insists that atheism/secularization is a necessary element within his ideology and enforces it as such, there would seem to be at least partial
sine qua non causality. That’s relevant, because the OP’s opposition portrayed atheistic ideologies as if they just
happened to be atheist, as if the atheism is always entirely incidental.
Anyway, I did outline a case for the correlation you seek in my earlier posts – in the huge chunk you failed to address. See: “immanentizing the eschaton”. I mostly allowed a prominent political philosopher to make a case for me. Lazy, I only plagiarized, offering but a couple broad suggestions; however, the logical connection is there to fill in with details, and you didn’t even broadly suggest why the proposed link might have no basis in fact. This connection would make a lot more sense if mankind has a basic religious instinct written into his DNA or otherwise inherent to his socio-political behavior (for instance, if tribal/civilizational success largely is propelled by or requires shared “religious” belief/custom).