Funny I do think its a mixture of biological factors and also a more pshychic/spiritual affliction.
Biological factors matter a great deal since, for example, the more dopamine in your brain the more receptive people seem to be to 'voices'. Many medications for schizophrenia aim to reduce the amount of this chemical in your brain, and it works, I am living proof.
However its all fine and dandy to say its ALL a chemical imbalance but this is not my belief. I do believe there can be other forces at work. Whether its all down to chemical imbalance that we have little control over these unwanted voices, I not sure. Wish I knew the reason why we get this.
Hmmm how many times you wondered why the kid at school gets bullied? How many times have people wondered this? Cos they can? IS it as simple as this? Some forces like to bully, plain and simple. Some people are picked on, some are not, plain and simple. Why shoudl it be any different in spirit realms?
In my experience meds can be great btw, also I would say you don't necessarily need masses of the stuff for it to have an extremely positive effect on your mental health. Just cos you are living a complete nightmare and your mind has been totally taken over doesn't mean that you have to have TONNES of medication, just a little can go a long way to helping severe conditions.