Agnosticism is illogical. I'm not engaging in hyperbole when I say this; it's just that to entertain the possibility that there is a god is actually logically fallacious.
Theists make claims for the existence of god, but their claims have no facts to support them, and any evidence they do provide is generally unfalsifiable (unproveable one way or another).
However, religious mind-viruses are so persistent because few people realize that what they are doing is saying "Because you can't disprove it, you should accept the possibility that it's true."
Obviously, it's impossible to prove a universal negative within a logical framework given the limitations of human sensory perceptions.