The Reality of Racial Differences

The culture of the age that we live in is founded on a lie: racial egalitarianism. It is an article of faith in the West that all racial differences in abilities and personality stem from environmental, rather than biological, factors.

This dogma has been conventional wisdom among the Western elites since 1950, when the United Nations published its “Statement on Race,” which declared: “There is no proof that the groups of mankind differ in their intelligence or temperament. The scientific evidence indicates that the range of mental capacities in all ethnic groups is the same…. Genetic differences are not of importance in determining the social and cultural differences between different groups of Homo sapiens.” Link, p. 102.

In succeeding years this belief has entrenched itself. A 2003 documentary on PBS, entitled Race: The Power of an Illusion, expressed a view that is more or less entirely unchallenged today in the media and most of the academy: race is a myth constructed by whites to justify colonialism and slavery. The documentary urged viewers to take an environmentalist view of racial differences:

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Source: http://inverted-world.com/index.php/articles/articles/the_reality_of_racial_differences/

>>5
Established organised religion is necessarily conservative or regressive, and actively opposed to change and evidence-based reality. It would have died out centuries ago otherwise.
The answers you seek are in memetic theory.

Atheism in the US (not "the West", just the US) is associated with progressive politics simply because the US has no sense of political balance anymore. American conservatism nowadays is knee-jerk reactionary ignorance, and farther to the right than anything the rest of the West has. That kind of ignorance requires religion to keep alive, because religion has much more experience with it.
So if you define "the left" as being the Democratic party, then yes, nearly all atheists in the US are "left-wing".

In reality, though, American atheists too span the spectrum from left-wing to right-wing. It's just that Republicans are so ridiculously far to the right they're fucking up your sense of proportion.