Why Be an Atheist Rather Than a Pantheist?

I keep coming back to this question. Richard Dawkins, in his book The God Delusion, says that pantheism is just “sexed-up atheism” (p.40).

I have never been able to grasp why someone who believes this would choose atheism over pantheism.

Seriously, if you had a choice between anything, and that same thing sexed-up, which would you choose?

I would like to hear from those who identify with one of these categories or the other on why you self-identify as one rather than the other.