"Tenets"

Earlier, I read a reference to the "tenets" of atheism, and though it is not at all unusual to speak of tenets, I was struck anew how strange the idea is.

I have two issues with the idea of "tenets" of a social movement.  First, I don't think there is any non-arbitrary way to define what a social movement is.  It is not the case that social movements have specific and well-defined beliefs. There is no objective answer to the question of whether any particular individual is part of the movement.

Second, I don't believe in a foundationalist worldview.  We do not start with assumptions and then build upwards.  Social issues are not mathematics.  Instead, we have a web of ideas which connect in all directions, up down left right in out.  We can easily observe that many people in a social movement share similar webs of ideas, but there is no "basis" which defines the movement.

Even Objectivism, which explicitly purports to be based on a few basic axioms ("existence exists" and other vapid statements), does not really have a basis which defines it.  If someone agreed with the axioms but disagreed with everything else, that does not make them Objectivist; if someone quibbled with the axioms, but agreed with the philosophy built on them, they're Objectivist as far as I'm concerned.

So it is true that most atheists don't believe in gods.  But there are also people who have complicated feelings about god beliefs, and yet still agree with the goals of the atheist movement or participate in atheist groups.

This is not hypothetical.  I've met plenty such people in meatspace groups, and often I have trouble remembering who exactly considers themselves "technically agnostic" or otherwise.  That they disidentify with atheism indicates a point of disagreement between me and them, but there are so many points of disagreement to speak of, and this one isn't special just because of its implications on the word "atheist".

Similarly, there are plenty of atheists who I don't consider to be part of the atheist movement or who are only distantly associated with it.

I would not speak of the tenets of a social movement.  Instead, I would speak of organizations, communities, media outlets.  I would speak of common (but not monolithic) beliefs, values, and goals.