Like most Americans, I grew up in a Christian household, and like most children, I never questioned the things I was taught in church--much like I'd never questioned the existence of Santa Claus, either. Adults tell you something is true, and you tend to believe it, particularly when everyone tells you the same story. All those authority figures can't be wrong, can they?
To make a long story short, by the time I'd reached my own adult years, I'd already begun to question the tenets of a belief system I'd been told was true all my life. What about other religions? Who decides which is "right," and why? What about people who never are exposed to the "right" religion--are they damned for their innocently-ignorant beliefs?
But what really pushed me off the edge of the cliff of theism and into that wild, scary realm of disbelief was my own strong foundation in science and reason. The whole flood mythology of the Bible's Old Testament simply cannot be reconciled with any notion of science, history, or reason; likewise, the biblical creation account contradicts science when taken as anything but allegory. Oh, I'd gone through the phase of creating my own epicycles, rationalizing six-day special creation and biblical chronology of a "young earth" which somehow meshed with the billions-of-years of age the Earth and broader universe clearly possessed, but dismissed those rationalizations before my teenage years had even passed.
To answer Ms. Christiana's question, I can even identify the exact moment I took that big, bold step over the theism cliff: February 24, 2002 (ironically, a Sunday), at the "Evolution vs. Creationism Debate" hosted by the Campus Bible Fellowship and Freethinkers at Virginia Tech. By then, I'd become an agnostic, but the exposure to the sheer intellectual dishonesty and self-deceit of the creationist speaker--and, in turn, the broader creationist movement--make up the proverbial straw that broke the camel's back.
The creationist speaker, Dr. Randy Guliuzza from the Institute for Creation Research (ICR), based his entire side of the debate around erecting a strawman of "evolution" which he then attacked, coupled with the false dichotomy of saying, "If you are wrong, then I am right." He didn't produce a single piece of evidence for his position (creationism), and when I called him on that during the question & answer phase, asking him point-blank to produce some evidence to support his argument, he simply responded that all he had to do was debunk evolution to prove creation (if you don't see the false dichotomy of that notion, I'm not sure I can help you).
Though Dr. Guliuzza couldn't replicate "Dr. Dino" Kent Hovind's infamous 300 creationist lies, his arguments did suffer from nearly 50 major problems in such a short debate, which I took down during the debate. He only had a couple of hours, so I guess he does deserve some credit for making that many mistakes, deceptions, misrepresentations, and outright lies during the debate (the numbers below come from the order he presented them in, as I listed them during the debate).
Some of his real laughers included defending creationism's validity by presenting public opinion polls (#1); claiming scientists have no "data" or "details" to support evolution (#2) because articles published in Discover and Popular Science lack them, as do books in the popular press (#3); that scientists condenscendingly think "you" are stupid (#5); appeals to authority ("Some scientists believe in creationism, so it must be true!" and "I have an M.D., so what I say about biology is true!") (#13 & #15); that evolution isn't "useful" (#12); and so on.
His strawman of evolution--a common tactic of creationists--included such ridiculous notions that evolution is "too broad" (#6) whilst simultaneously demanding it explain cosmogenesis (#23) and other aspects of physics, not biology, as well as areas of biology not remotely related to evolution, like abiogenesis (#22); and the insulting notion that "scientists say humans come from worms," (#27) and that "scientists have to use computer animations showing one animal turning into another" (#4 & #26). This is the same tactic Dr. Dino (who currently resides in federal prison, I might add...) uses in his "$200,000 challenge" whereby he claims he'll give anyone who can "prove" evolution a big sum of cash--yet they have to "prove" something not even remotely identifiable as evolutionary theory. Of course the audience (and even scientists) would agree his strawman "evolution" is no good... the problem is, it simply isn't evolution.
The whole notion of debates as "proof" of one's theory also irks me; creationists are good at winning debates with laypeople audiences, who quite honestly aren't capable of making a proper evaluation of the science behind evolution, and who may be easily swayed by the strawmen and ad hominem attacks of creationist arguments. "Show us the data!" the creationists cry; despite the fact mountains of such data exist in the academic literature or even a decent biology textbook, they claim victory when the scientist at the debate doesn't display table after table of mind-numbing data, even when refusing to produce any evidence in support of creationism itself (remember that false dichotomy I mentioned?)
Dr. Guliuzza went on to make several demonstrably false scientific statements as well; ever wonder why creationists spend so much time picking at evolution instead of layout out evidence for their own theory? It's because they can't do science, and what science they try to do is quite poor. For example, he claimed an evolutionary change resulting in a loss of functionality or information contradicts evolutionary theory (#28)--another straw in that big man-shaped bale of hay. He made the oft-repeated claim that "all mutations are bad" (#40); that bacterial antibiotic resistance doesn't exist (#35), that HIV has not and is not changing as a virus (#41), and several other real whoppers which simply are wrong in all factual regards.
Finally, creationists often accuse evolutionary theory of failings which in any sense actually apply more to creationism than evolution, and if to be taken as points against a theory, must condemn their own position! If evolution is "too broad" to be an acceptable theory (#6, an accusation demonstrably incorrect to begin with), what of the notion that "Goddidit" to explain everything, from cosmogenesis to abiogenesis to evolution and beyond? If evolution has "no predictive value" (#14, and again, demonstrably incorrect), what of the Bible and creationism?
Creationists claim scientists "force" data into "unnatural" configurations to support evolution (again, provably wrong, and #10 on Dr. Guliuzza's list of lies)--what, then, of all the epicycles invented by creationists to try to fit observable science to a "theory" broadly and wholly contradicted and disproven by said science? I suggest the interested reader check out the topics of "flood geology," "hydrological sorting," and the "vapor canopy," and get back to me on who exactly is forcing data into unnatural configurations--and afterwards, take a look at the ridiculous notions of variable speed-of-light ("tired" light is responsible for redshift, so says that "theory"), incredibly variable rates of radioactive decay only stable in the past few years (to explain away radioisotope dating, among other things), and mutation and speciation rates far in excess of anything evolution demands to account for all the biological diversity we see today having arisen a few thousand years ago from Noah and his rinky-dink Ark.
Looking back on my notes from that 2002 debate, I found this gem:
Finally, as I have indicated before and likely will again, isn’t it hypocritical for creationists to accuse someone else of using “just-so” stories (like, maybe, “God did it!”) to explain their position? Forgive me if I am wrong, but my exposure to creationism has left me with the feeling that the whole platform is based on one great big just-so story called the Bible.
Using that as segue back to my original topic of how that particular debate drove me away from theism one and for all, that day's events are what really opened my eyes to the particular sort of dishonesty (intentional or through ignorance; it doesn't matter) and refusal to partake in any meaningful discussion or rational argumentation about either science or religion that makes up not just creationism (and its "lipstick on a pig / monkey in a tuxedo" cousin, (un)intelligent design), but on a broader level religion as a whole. Religious beliefs are just that: beliefs. They cannot be supported factually, yet many of the claims of religion run counter to observable, factual science. When you scrape away all the fluff, all that's left is a warm fuzzy notion of "god," and to me, that's simply not enough to justify a belief in the face of all other rationality.