This is actually a good place to discuss the "empiric argument". Or Evidence of abscence argument
http://en.wikipedia.org/wiki/Evidence_of_absence .
If I said that a new species of bacteria existed on pluto, or as you put it a living (growing, reproducing) organism lived in the center of stars, we would both say that there is no evidence that such a thing exists, but I would not be able to say that such a thing is impossible. My first question would be why do you believe that one exists.
As for why people believe in the supernatural, it stems from two perceptions. Man's need to explain the world and man's need to explain himself.
The first we know is science. The latter is metaphysics. Why is it wrong to kill, to rape, to hurt others. Simple explainations said that these things were "evil" and in order to explain them we contemplated the existence of an ultimate judge. One that knew all and would punish these deeds. Modern atheistic explainations propose that such activities are counterproductive to civilized human interaction.
So the answer to my question is that for thousands of years man has contemplated the nature of his existence, one theory is that sentience is somehow extracorporeal and one is that it is not.
For an argument to support that something does not exist, one needs to find logical inconsistancies. For me the logical inconsistencies exist in the definition of god.