Are agnostic or atheistic Jews who use persuasion to attempt to convert practicing Jews to their systems of unbelief apostates?
Can you point to any real-life examples of this proselytizing agnostic or atheist?
Even if you can, there is a substantial distinction between questioning or renouncing "Belief A", and actively embracing "Belief B". An agnostic or atheist may lack belief in Judaism, but he has not actively accepted a different religion in its place.