Okay, so I'm jumping in. My take is a little different to those that have already spoken, or perhaps rather my background (being an atheist) combined with my answer is a little different.
Definition
I like Hitchens, for a bunch of reasons (entertainment value amongst them) and his definition makes some sense to me, so I run with the following;
I am not even an atheist so much as an antitheist; I not only maintain that all religions are versions of the same untruth, but I hold that the influence of churches and the effect of religious belief, is positively harmful. Reviewing the false claims of religion I do not wish, as some sentimental materialists affect to wish, that they were true. I do not envy believers their faith. I am relieved to think that the whole story is a sinister fairy tale; life would be miserable if what the faithful affirmed was actually true.... There may be people who wish to live their lives under cradle-to-grave divine supervision, a permanent surveillance and monitoring. But I cannot imagine anything more horrible or grotesque.
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Thing is, I'm pretty much right there with him. But I don't class myself as an antitheist, and wouldn't. I have a negative take on antitheism, and I'll try to explain why in point form. But first, I think it's worth explaining what I DON'T think antitheism is.
- I don't see antitheism as the violent or even loud denunciation of theism. I imagine some antitheists are quite reserved, or even private in their belief that theism is harmful.
- I don't see antitheism as a belief that theism is necessarily massively harmful. Some antitheists likely see it as merely less preferable than an absence of theism.
- I don't think antitheists are necessarily angry about anything.
- I don't think antitheists are necessarily looking to control theists.
So why not antitheism for me? Simply because I think painting a broad brush over belief falls into the same incorrect (if understandable) assumptions about belief that theists seem to be painting about antitheism. Take a large group of people (and we are talking seriously large, over a lot of cultural, gender and age demographics) and make statements about whether they are good or bad and you are neccessarily wrong (in my opinion).
Anti male, anti female or anti white, anti black, anti old, anti young...heck pro any of those things too, for that matter.
I generally like to test my beliefs by checking the inverse, and seeing how it fits. Anyone who thought theism was good would be delusional, or simply operating at helicopter view, to my mind. There are too many flavours of theism. For exactly the same reasons, I don't paint pictures about theism as a whole in a negative light. Is it right for me? Hell no (pun sorta intended), and I have a lot of issues with much of the more visible religions. But belief, as a concept, I could care less about. The effect of that belief is a different story.
As a final point, Quintessence raised a variant of a view I subscribe to.
She mentioned that antitheism is a good way to put offside potential allies (and I'm paraphrasing to a massive degree). I suspect that the very point of antitheism is to suggest that there IS no good theism, and I have some sympathy for this view. But I do see plenty of theism or belief (more generally) which doesn't effect me in the least. I have no interest in even suggesting the removal of this from the world would make any difference. Panentheism...couldn't give a rat's tossbag. Secularism is more important to me, and a panentheist could be an ally in this (or not). I find it counterproductive to waste a moment wishing away theism when I could more productively use it wishing FOR secularism.
Just my take. I don't have a massively strong opinion on this, to be honest, but I thought it worth offering up a slight variant of what's already come.