Why a heaven and hell couldn't exist.

[Iroscato]

It's pure fantasy, with absolutely no relation to anything real anyone has ever experienced...That is the difference between science and religion: science makes testable, falsifiable claims. 

Firstly an afterlife has been experienced by real people during NDE's. Repeated studies by respectable researchers like Van Lommel, have clearly demonstrated that NDE's are what they appear to be. Secondly, Swedenborg was a real person who experienced both Heaven and Hell for extended periods of time and gave first hand reports of the things he saw and heard.

So a few people's recounted experiences during times of severe oxygen deprivation mean we have to rewrite everything we know about physics and the nature of reality in general?
Mm, nah. Fortunately, we know how damn good the human brain is at seeing and experiencing what it wants to see and experience. This is why things like the placebo effect exists.
If there is a God, an afterlife, any sort of supernatural shephard of the universe in any way shape or form, then they should really stop being so damn shy and reveal themselves to us, instead of dropping very vague, insubstantial breadcrumbs to those whose brains stop working for a bit.