(Note – Edited as of 11:35 PM, when I came across a better way to phrase my original thoughts.)
I've been thinking alot lately about "evidence" for God's existence (and the inherent lack of it), and now I've finally determined what I believe truly is the ultimate, irrefutable bit of "proof" (or as close to proof as it gets) for demonstrating, once and (perhaps) for all, that God doesn't exist. (Note that this only applies to the Christian God of the Bible, though I suppose it could also apply deities from similar molds).
Of course, the Christian God is, by all means, "perfect": knows all (omniscient), wields unlimited power (omnipotent), is everywhere at once (omnipresent), and most importantly, loves all (omnibenevolent). These are the qualities that are predominately set forth via the Bible (disregarding the contradictions for a moment) – which, remember, is regarded as being his own Word. Everything in that holy book is the perfect truth: immutable, never wrong, etc.
With that framework in place, I now present you, rather than a laborious explanation from my part, a famous quote from the Greek philosopher Epicurus:
"Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?"
Many of you will have heard or read this before. It's likely; my only problem with it is, how come it isn't spread around as widely as it should be?
I mean, just think about it. This short little paragraph contains what I personally consider to be the ultimate "proof" that God doesn't – or at least, can't, judging from the very Bible he declares holds his own Word – exist. It's perfect.
"Evil", as is used in this quote, represents all things dark, horrible, painful, tragic and suffering: death, torture, destruction, war, rape, what have you, that exist in the world. All the things that keep his Creation from being a true "heaven-on-Earth", so to speak.
I've heard several arguments against this, and as far as I can tell, they all fail for varying reasons. Most of them, unsurprisingly, are variants of that old maxim, "The Lord works in mysterious ways" and so forth. That he and his methods are ineffable, that we little humans cannot comprehend the might, the scope, the [etc.] of his plan. Okay, I'm willing to go along with that – no-one claims to be perfect to to understand things that, for now at least, cannot be understood by the modern human mind. (And I'll neglect to elaborate over how odd it is that a perfect God needs to be so sneaky as to keep us all in ignorance about plans. Even if he were afraid we might undo them should we learn, that's a moot issue as, seeing as he and his plans are inherently perfect, we couldn't undo them no matter how hard we tried.)
But what I have a hard time following with this argument is how, even if we humans cannot always understand God's logic, God seems notoriously willing to defy even his own logic as set forth in the Bible. Examples are too numerous to detail here; just take, for example, how despite supposedly loving everyone equally and completely, he seems remarkably quick to deliberately inflict suffering, destruction and death upon his people – burning down cities, flooding the entire world, and so on. It's one thing to allow humankind's inherent capacity for evil and dark deeds to run rampant, basically allowing humans to harm themselves, but to intentionally kill and torment his own beloved people via his direct actions – burning them, flooding them, etc. – makes it sound like he has a horrific case of Bipolarity. At best.
Another argument I've come across is this one, from Makarios:
This, I believe is perhaps the single greatest reason for why God allows suffering and tragedy to take place. These things solidify our opinions about God. Suffering causes us to either reject God or humble ourselves before God.
Anyone who reads into this argument will quickly realize how patently absurd it is. It is wrong on numerous levels: it implies that God intentionally inflicts suffering and tragedy to force us humans to form an opinion of him (as if we were unable to form opinions of him, or anything else, otherwise); it implies God is desperately seeking his people's views of him (which is a surprisingly needy trait from a supposedly omnivalent deity); it indicates that he is willing and able to inflict torment upon his supposedly beloved people (which is cruel); it also implies that we can only form a concrete opinion of him when we're undergoing suffering and tragedy (which ... just doesn't make any sense at all).
Yet another argument I've heard, actually comes from my own mother (though I'm certain many would think along the same lines). To put it in short, she said that perhaps the reason God would allow pain and suffering amongst his own beloved people, is basically to let them "evolve" (as in spiritually, morally, etc.), to let them learn from their own mistakes as they grow more and more advanced and sophisticated.
I'll admit that at first I was honestly stumped by this comeback (she often does get me when I don't expect it, hee ...), but the more I think about it, the more I realize it doesn't hold up to God's logic, either. Remember that this is an all-loving God, as well as one who's all-powerful (tired of hearing me repeat that already?). It would be obvious to any thinking person that any God who is able and willing to "impose" a perfect world upon his people, one that is without fear, pain, destruction and suffering – without evil, basically – would be expected to do so. Not doing so would be pointless; why allow his creatures to slowly (very slowly) evolve their ways into lesser evil and suffering, when he had the power to instantly end it all and give them safety and happiness? What good reason could their possibly be against this? Not doing so at once would only indicate he actually enjoyed watching humans spread suffering amongst themselves as they (ever-so-)slowly evolved ... or else, that he simply didn't care. Which are two traits that would instantly tear down the Christian image of the perfect and infallible God.
God simply cannot exist if he violates the very rules of logic and sense he himself supposedly established in the Bible (his Perfect Word). If there's anything he cannot do, he's not omnipotent. If there's anything he wouldn't do for the benefit of his beloved people, he can't be called omnibenevolent. If he doesn't know everything or is surprised by anything, then he's not omniscient. And so forth.
I happily invite any Christians who are patient or bored enough to be reading this blog (much less this post) to enter the comments section and tell me why, exactly, God would allow evil to run rampant amongst his Creation and people if he was both willing and able to eradicate darkness and misery. I welcome a debate – I've been missing a good one these days.
 Keep in mind that my mother is very strongly anti-religious, perhaps even more than I am, and absolutely does not believe in the Christian God (though she does believe in such things as the Law of Attraction ...).