Many people choose not to worship any deity at all. This is not seen as evil (though it is mildly chaotic), but priests focus a great deal of effort on converting these non-theists.
Antitheism is the related but distinct position that deities should be opposed, by various means, often on the reasoning that mortals should be free to choose their own paths, or that the transactional relationship between worshippers and deities is an inherently unfair one.
A secretive, extremist antitheist organization known as the Defiance exists, dedicated to the outright eradication of all gods. The organization is currently led by a master vampire wizard known as Cofniben.
Antitheists are never clerics, paladins, or favored souls, and are rarely druids or rangers. They are frequently ur-priests or defiants (Planar Handbook), and sometimes paladins of freedom with ACFs that trade away divine spellcasting (Unearthed Arcana).