Atheism is related to the question of theism, but it isn’t a religion.
To understand atheism, you would have to understand the definitions of what theism and religion are.
Theism by definition is a belief in the existence of a deity or deities.
Here is the definition from Oxford dictionary:
Religion is about believing, following and worshipping deity or deities:
The definition definitions are in bold, the rest of the text after the colon “:” are just examples of usage of the dictionary terms.
The key word in religion, apart from “belief” and “faith”, is “WORSHIP”.
Atheism deals with the question about theism, thus they don’t believe in a god or gods.
But atheism isn’t a religion, because atheists DON’T WORSHIP any deity.
I don’t really care what your Supreme Court say, because atheism don’t worship any god that they don’t believe in.
You are not using your common sense, whirlingmerc.