(1) I am not assuming that we are just physical beings...It is a fact...On macroscopic level, we know with a high degree of confidence how electron, protons and neutrons behave...
We know the forces that dictate the behavior of atoms on an "everyday life" level...
(2) The evidence is as concrete as it gets...The only thing that exist is the physical human being...Even the human "mind" is not a mystic...It is the physical activity of the brain...
Life on Earth comes down to a series of chemical reactions and mixtures...
(3) As neuroscience keeps developing, we will know even more about the brain...And even more superstition will be proven wrong...This the trend I am basing my projections on...
When humans don't understand, they create a mystic, then a scientist comes along and explains the phenomenon, and we move on to the next mystic...
(4) I have worked with people suffering from mental illnesses and Alzheimers/Dementia...When you lose enough neurons and/or your neurons stop functioning properly, you get 'demonic possession'...
If you see a psychotic patient, then it is not hard to imagine why people 2000 years ago will use demonic possession to explain the erratic behaviors...
I have seen an old lady become catatonic, and then the same lady after a few sessions of electro-convulsive therapy...The change is a MIRACLE...
Just more evidence that there are no souls/spirits...You have a mind which is a function of the brain...Thus, it is PHYSICAL...