I freely admit that not all of my hate is for good reasons. For example, I hate the sheer number of cliched arguments involved. I hate analogies about baldness, collecting stamps, and fairies. I hate distinctions between lack of belief and belief of lack. I hate arguments over negation and certainty, even if they happen to be good arguments. As for this diagram...
I have seen so many variants on this diagram. (Source)
...I think it needs two more dimensions.
The horizontal line in the middle represents people who think that there is no way to tell whether the diagram is or is not BS. ...with apologies to the creator of the original.
These are silly pet peeves of mine, but I think there are also some good reasons to dislike arguments over atheism/agnosticism. I believe that the arguments are mostly made of relative opinions. That is to say, identifying as agnostic or atheist mostly has to do with how you see yourself relative to others. Are you constantly bothered by those atheists, or are you sick of those agnostics? It's all about who you want to use as a foil to yourself.
And since the arguments are primarily about your personal experiences and impressions of the other side, it all ends in stereotyping.
Supposedly, agnostics are accomodationists and atheists are more confrontationalist, and this stereotype is the basis of much defense and criticism of agnosticism. But the stereotype simply isn't reflected in my personal experience. Many agnostics I know are aggressive critics of religion. I suspect this may be most true in the atheist community, where the agnostics are usually outspoken contrarians. I do not think my experience reflects any general characteristic of agnostics, but it makes me think the stereotypes are unfounded.
Often, these stereotypes are encoded in the definitions. For example, agnostics sometimes define agnosticism as lacking certainty about God. The implication being that atheists are 100% certain and dogmatic, or they're too stupid to realize that they're actually agnostics. Atheists sometimes use a broad definition of atheism, with the intention of arguing that agnostics are either religion-apologists, or too stupid to realize that they're actually atheists.
There's supposedly a substantive issue underlying atheism/agnosticism arguments. That is, is the existence of god discernible? Agnostics say no (unless you're talking about the silly sky-daddy kind of god). Atheists say yes (unless you're talking about the useless deist kind of god). This supposedly substantive disagreement, when properly understood, boils down to what kind of definition of god you think is most relevant. That is to say, the disagreement is not all that substantive. I'm not convinced that the substantive gap between an atheist and an agnostic is any larger than the substantive gap between two agnostics.
And I can't say I really care about this hair-splitting. Virtually every other issue which people argue over, they don't worry about degrees of certainty. For instance, why don't people argue over whether they're certain about the success/failure of the free market? It's just this issue, and you hold one position or another, or you don't argue either way.
I identify as atheist because I wish to take a position against religious beliefs. I don't identify as agnostic because that is a game I refuse to play. When I find that other people identify as agnostic, atheist, or agnostic atheist, I don't ask why, because I'm sick of hearing about it.