Why do atheists deny that they are just biorobots?

[FatAndFaithless]

I believe the point is that their theism is the source of those beliefs, whereas atheism is one result among many that is arrived to through investigation of the world.

My point is that a belief can be both the conclusion of prior reasoning and the premise of continued inquiry. My detractors refuse to acknowledge the first in my position and the second in their own.

I can see that, but I don't think atheism quite has enough...substance? to fit that sort of premise. There simply isn't any sort of method in atheism that suggests a way of investigation. It's true that I might be more likely to reject theistic or supernatural claims out of hand than a theist might, but I would chalk that up to the skeptical and empirical methods that I employ (or attempt to employ, anyway), not to my atheism.