A friend of mine in Buffalo, the son of a Methodist preacher, labelled me as the only “evangelical atheist” he'd come across. I was young then. As part of the conversation, he offered me an “out”: Wasn't I an agnostic, or skeptic? I responded that for me as a scientist it would be a cop-out to be just agnostic or skeptical in the face of the overwhelming lack of evidence in favor of … whatever it is that is not out there. It is true that being skeptical or agnostic about WIITINOT, fairies or the Great Halloween Pumpkin is not quite the same as being skeptical or agnostic about say the ether or caloric. The theories of the ether or caloric made clearcut predictions (which were then falsified by counter-evidence), unlike religion or String Theory. So the existence of WIITINOT has not been disproven, nor can it be. It is just that the evidence in favor is … underwhelming, and I invoke Occam's razor.
Now that only explains why I am an atheist as opposed to an agnostic or skeptic – it does not serve to functionally distinguish between an atheist and an agnostic. I asked myself what it is that makes me an atheist. An agnostic or skeptic is open to the possibility of admitting the existence of WIITINOT, and hence one can (and should) ask of an agnostic what it would take for her or him to admit the existence of WIITINOT.
I am only agnostic implies that there exists some hypothetical event which would leave me no choice but to admit the existence of WIITINOT.
In my case, however, there is absolutely no imaginable event or series of events that would force me to accept or even suggest to me the existence of WIITINOT. This is not to say that there are no phenomena that I can't explain, nor that if something mysterious were to take place in front of my eyes I would be able to explain it. I would be happy to admit my personal ignorance, but before attributing the event to some WIITINOT, I would be assured that some human either already can explain it naturalistically, or that in the future humanity would eventually be able to explain it naturalistically. After all, none of us understands derivatives (the financial instruments, not the calculus kind), but we don't usually invoke them as evidence in favor of the existence of WIITINOT.
400 years ago no human being understood the rainbow, and it was an ineluctable mystery attributed to WIITINOT. Now, the immense majority of even us educated humans still can not explain the rainbow (nor even describe it fully), but it is no longer a mystery that necessitates the existence of WIITINOT, we all know that there is some human being, likely a physcist, who can explain it fully.
I repeat, there is absolutely no imaginable event or series of events that would force me to accept or even suggest to me the existence of WIITINOT. By modus tonens, I am not only agnostic, I am a full-blown, unremediable closed-minded atheist.
That doesn't prevent me from being friends with NAIFs – NonAtheistIntelligentFaithers. (My friend dissuaded me from referring to nonAtheists as “credules”.) Witness my friendship with Cosmic, who is a christian. On the morning after the day I met him in Las Vegas, in his pickup truck on the way to climb, I noticed a handsewn dashboard cover, a wooden cross mirror ornament etc. I asked him and he explained, that he was a christian (Christian?), that Jesus had walked this earth, that he died on the cross for us and that his love for us … that Cosmic felt Jesus' love for him, as he felt Jesus' love for everybody and that he hoped I wouldn't mind his talking to me about Jesus, because he would. I told him I was an atheist and I didn't mind at all, I would love to hear what he had to say as long as I could ask questions and discuss things, but that there was nothing he could say that would convert me and that I was not looking to convince him either. Cosmic said very slowly that was fine, he just felt compelled to talk because he felt Jesus' love.
So later that day when I slipped on a hard move, 15' off the deck, and nearly fell, and managed to make the two or three moves up to the large hold, and looked down at Cosmic with relief and pride and then exclaimed upwards, Thank You Jesus!, Cosmic understood me, you'll be a Believer yet.
And when he called me this week to tell me that his prayers would be with me, I understood him, and was able to honestly tell him that my prayers would be with him during his shoulder surgery.
I have two take-aways: One, agnostics and skeptics should be challenged to state the conditions under which they would admit the existence of a WIITINOT. Two, if you are inflexible, decided, obdurate etc., you should declare yourself as such before entering a discussion.