How can people claim that atheism is not a religion?

Your problem is the definition of religion. It speaks of FAITH which is something a non-believer does not have. There is no atheist pope. There is no atheist priest. There is no atheist church. There is no atheist organization of ANY kind. So, HOW can you claim a non-belief or lack of a belief system is a religion? Your "Miriam Webster includes this" is bogus because it is not a prime definition or even a secondary definition, but an OBSCURE use, and really falls down because it includes the word FAITH. Atheists have NO faith, THAT is the problem with this obscure definition, the square peg you are trying to fit into the round hole. By the way, I do NOT hang around R&S. I see these questions on the home page. The questions that idiots post trying to bait others who do not believe as they do, find ME... You are no exception, so you can NOT lump ME in with the "pack of dogs" you refer to just because I choose to NOT believe as YOU do. YOU use the words, "ardor and faith", NOT ME. I do not have "ardor and faith" at all. I am simply a non-believer. It is religion that makes the claim that there IS a god. I challenge that claim. I take it as seriously as a charge of murder and I ask for the same level of consideration, using evidence to back the claim. Something MORE than just your word, a smoking gun. So just show me that smoking gun that backs this claim and proves the existence of your god. I make NO claim about god, yours or anyone else's. I do not say a god is impossible. What I DO say is I see no evidence that supports YOUR claim. For all I know, there MIGHT be a god or a god-equivalent out there somewhere in the infinite vastness of the cosmos.