Ybe an atheist

[Ybe]

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A-squarism is the default for anyone that doesn't believe in any Squares.
  vs
 A-squarism is not the default for anyone that doesn't believe in any Squares.

Same problem... that's the point of my analogy. 
It's like you're saying that not collecting stamps might not be the default position for not collecting stamps. Or saying that bachelors might not be unmarried or squares might not have four sides.

The point is that atheism has to be the default position for atheists.

Perhaps there is some misunderstanding>
  So, the default position is simple to see.

Belief in No X-rays vs  belief in X-rays  What is the default postion?