Comment 4 by Absinthius :

We really need to stop letting them get away with the assumption that, like with religions, atheists are a likeminded movement.

Atheism is the ABSENCE of ridiculous superstitions, everyone who doesn't believe in superstitious nonsense can call themselves an atheist, there are no other criteria, no people who make rules to decide who gets to 'join the club'.

Exactly the same what that everyone who isn't a neurosurgeon is an aneurosurgionist... or whatever the word can be. There is no way you can generalize aneurozurgeonists... on any bases other than them not performing neurosurgery on a regular basis.

Of course anyone can become an atheist. That's not what Jen is discussing here, though. Her article, and the article which inspired this response, are about the atheist movement (activism that is driven by a person's atheism), not atheism itself.