Disclaimer: Depending on your definition of atheism and agnosticism, I may actually be advocating agnosticism in this text. These two terms have any number of definitions and what follows simply reflects my perception of them. The point is not that one term is better than the other. What I'm trying to argue is simply that one type of thought process associated with agnosticism is not particularly useful.
The more I think about agnosticism the more I think it's just the politically correct face of atheism. It's a way to say "Hey, listen guys, you say you know god exists, and we're skeptical. But that doesn't imply we think we're better than you, we just think it's impossible to know at all." That is the gist of it, but does it really differ from the atheist position in any important way? I don't think it does.
Does an agnostic believe in god? If he did he would be a believer. Which he isn't. So the answer is no. Of course, the agnostic slogan is "I don't know", but in a question of belief, there is no such thing. There is no way to not know if you believe in something. You either believe or you don't, and if you "don't know" that means you don't. You fail to give a positive answer.
The problem with agnosticism is that it gets you into meaningless statements about probability. An agnostic who adamantly repeats "I don't know" is likely to be seen as low hanging fruit for believers and unbelievers alike. "Okay then, what do you think is more likely?" Agnostics in their drive to be even handed get pushed into saying that both are 'equally likely'. Well, what on earth does that mean? Is that a statement about statistical probability? So in a repeatable experiment where the universe is created god appears 50% of the time? That's absurd reasoning. We are not talking about something measurable and therefore there is no way to say 'how likely' it is.
Wrong question, wrong answer
A philosopher once said "as a philosopher it is not that I can produce more answers, but I can make sure we don't ask the wrong questions".
Religious people claim to know with absolute certainty that god exists. And thus they seek the equivalent answer from the unbeliever. "Can you say with absolute certainty that god does not exist?" It is the wrong question. And to see why we need only ask a different, obvious, question. "Is there anything at all you believe with absolute certainty?" Again, the answer is no.
What does 'absolute certainty' even mean? It would have to mean, I think, that notwithstanding circumstances you know nothing about, your faith would still hold. If nothing else, that strikes me as just about the most foolish statement imaginable. Religious people claim to have this certainty, and that's their business.
In any case, we know that life is unpredictable, and it is possible that anything one has established as knowledge may be overturned. Is there any knowledge at all you have that holds beyond the constraints of sensory perception and reason? No, there isn't. Everything is theoretically subject to change.
So why on earth should I have to answer the question of god to a greater degree of certainty than I have about any other question in life? Agnosticism exists only because we need an answer to this incorrect question.
Atheism is the realization that the question is incorrect. An unbeliever simply does not have an equivalent answer to the question of absolute certainty. Atheism is not about absolute certainty, it is about giving an answer to a question that has a reasonable answer. Does god exist? No. Do you know this with absolute certainty? Irrelevant. I know god doesn't exist with the same certainty that I know Superman doesn't exist, and that's perfectly sufficient.
Atheism is the realization that the difference between a hypothetical "no" and a practical "no" isn't worth dwelling on. Because when it comes down to choosing how to live life, there is no agnostic option. You either live your life according to religious observance or you don't. No agnostic will sit in the 'waiting room' until the answer comes in. Thus there is no practical difference between the agnostic and the atheist, only a theoretical one.
This also resolves the misunderstanding that "atheism is faith just like theism". Atheists do not have an equivalent belief, that is what the a in atheism means.
Political correctness
How does political correctness factor into it? I think the answer is obvious. Religion is such a big issue in our culture that we have the intuition not to take these questions lightly. Religion is not just an issue of faith, it's also a question of world view, of social institution, of tradition, of family ties. To reject the god hypothesis is to reject religion, because what sensible religious observance could follow if you eliminate the cornerstone of religion itself? And to reject religion is to make a big life decision.
That is the paradox of the god question. The fallout may be complicated, but the question isn't. So people hesitate to say what they would so easily say if it wasn't for the collateral damage.
To say "I don't know" to a question of belief, I think, is to say "I don't believe, but I'm not sure what the consequences are going to be". We are not so hesitant to answer other questions of faith. Do people say "wait a minute, you can't be dead certain that Superman doesn't exist"? Actually, I can. He's a fictional character from a comic book. Do I need to be more guarded in my reasoning? No, I don't. I'm never going to get a more useful answer than "no".
Are you still on the fence about Santa Claus? Of course not. Because there is no reason not to say just say "no".