[boomboomsubban]

Masons require a belief in a supreme being and scripture, and various things online say they've explicitly forbidden atheists before. I take everything I read about Freemasonry with a grain of salt, but it still seems fairly hostile to atheists.

[wl]

You're correct that Anglo-American Freemasonry requires a belief in a Supreme Being. However, the issue of scripture is a bit more nuanced. There's no requirement to believe in the veracity or to honor any scripture in particular. There is a Holy Bible on an altar in a lodge room but it's used as a symbol. During an initiation, a candidate usually has the option to use the holy book of his choice. If one is opposed to the idea that holy books should be honored at all, he might not be a good fit for the institution, but there's nothing technically preventing him from joining. There's also a few times when portions of the Hebrew scriptures are read aloud, though they're pretty unoffensive from a universalist perspective.

[boomboomsubban]

They seem to be somewhat welcoming towards most major religions, but atheists still seem frowned upon. One could argue that the universe itself is a supreme being, but any scripture put forth would likely raise some questions.

I'm sure an atheist could successfully become a member, but I doubt many are trying to as the original post joked.