How do you suggest they impartially investigate NDE's 'scientifically'?
Search for external factors that could be affecting the brain - monitor brain function to look for activity that appears to be spontaneous, or at least that appears to arise differently to brain activity under other circumstances. Investigate.
How do you propose people impartially investigate them, or indeed anything else, without the scientific method?
Merely by assuming that they are brain generated hallucinations....??!!
No, by presuming that the experiences are caused by something, and running through the viable possibilities to determine what has a) capacity and b) evidence of actually existing. Of those, test and trial between them to see which is the most likely, and adopt that as the working hypothesis until further evidence comes along.
From that evidence it would seem that these are, effectively, hallucinations; they are mental states that arise, possibly from the breakdown of brain biochemistry under unusual circumstances causing 'misfires' of neurons, as a result of ischemic damage in the brain. There is evidence for the biochemical breakdown, there is evidence for the ischemic damage, there is evidence of the spurious neuronal activity... what there isn't any evidence for is 'soul'.
If you want 'soul' to be in the mix, how do you demonstrate it? If science isn't your preferred toolkit, what is?
O.