You have a very peculiar way of using words. You seem, somehow, to be putting a wall up around your notion of what "belief" means. The reasons for it remain completely opaque to me.
A "proposition" is "a statement that expresses a judgment or opinion." In what way, exactly, are judgments and opinions so very different from beliefs? Whether I believe the bus will be along in 5 minutes, or I'm of the opinion that it will be here in 5, really are quite the same thing, in the end.
Wikipedia defines atheism as:
"Atheism, in the broadest sense, is an absence of belief in the existence of deities. Less broadly, atheism is a rejection of the belief that any deities exist. In an even narrower sense, atheism is specifically the position that there are no deities."
It is all of those things, depending on the atheist. So who are you to try and redefine it for the rest of us. You do not speak for me -- nor for my beliefs, unbeliefs, opinions or judgments. My atheism means what
I SAY IT MEANS TO ME.