Falling in the mixed viewpoints of Archaists, Idolists, and Atheists, Agnostics choose not to place their faith in any particular religion or god as they are not certain on a subject's existence. There may be a spiritual energy out there, but in an Agnostic's eyes, there is no sound proof, regardless of what is written in Khy'eras' history books. Therefore, these people choose to leave their options open, so to speak.
Not all beings on Khy'eras have a practiced faith; some believe in "nothing". Meaning, there are folk that go about their lives without praying to an Eidolon or Idol. This certainly does not mean these people are evil; they rationalize that their fate and paths belong to themselves and no one else - especially not unearthly deities.
In response to what has been recorded in Khy'eras' lore, Atheists can agree that Eidolons were present in Khy'eras' past, but that they were just another race that had exceptional powers and are unfortunately, now extinct.