The equivalent of "it's never aliens".
There might be an afterlife or not. But in order to accept this idea as true, a proof (extraordinary one in that case) is needed. And for now, except some anecdata, there isn't much to it (as far as I know).
The basic principle is falsiability. It has been widely established that a sufficient condition to alter or eliminate consciousness and even personality traits is inflicting precise physical changes to the brain, such as severing pathways.
There is absolutely no evidence, let alone reproducible observations, supporting crackpot theories such as afterlifes or any form of consciousness that is not dictated by the brain.
It makes absolutely no sense to appeal to this or any other form of crackpot theories by alleging that established facts and knowledge covered by mainstream theories is still under development.
To assert that atomic activity dictates the bounds of consciousness sounds a lot more like asserting the moon is made of cheese than entertaining the possibility that it isn’t. We didn’t even understand basic atomic principles until Rutherford et al around 100 years ago, and our knowledge regarding neutrinos and particle acceleration is still rapidly evolving.
To claim that because we have not directly witnessed or extra-physical consciousness is a bit like saying a grain of sand is the smallest unit because we haven’t witnessed anything smaller.
This assertion is rather short-sighted and presumes, wrongly, that knowledge on a topic is already complete.
Yet, we live in a day and age when scientists are still discovering muscles in the jaw. We're talking about basic anatomy, not how neurons work.
https://news.ycombinator.com/item?id=29705819
Is it too hard to imagine that knowledge on how the brain actually works is still far from complete?