You misunderstand schizophrenia. There's no evidence, as far as I am aware, that schizophrenia is a result of brain damage. There seems to be a genetic link to schizophrenia. (
http://www.schizophrenia.com/research/hereditygen.htm)
Schizophrenics cannot distinguish between fantasy and reality. When they hear voices, its usually just their own thoughts. We (non-schizophrenics) are largely unaware of just how many internal dialogues are going on in our heads. Normal people have filters to quiet these "voices".
When a normal person goes into say, a crowded restaurant, their brains have a natural filter that filters out all other conversations going on around us. This allows us to be able to focus on our immediate surroundings, the person we are talking to etc. A schizophrenic does not have this filter. When they go into a crowded restaurant, they are unable to naturally filter out all other conversations. They can simultaneously hear the conversations going on at the tables around them, hear the cooks in the kitchen etc. This same filter is responsible for drowning out the voices in our heads. This is why schizophrenics have such a difficult time concentrating on things. Imagine how massively overstimulating even the quietest environment would be if you were unable to filter out everything going on around you. A quiet evening in a coffee shop would be like a rock concert
As far as the inability to distinguish between fantasy and reality, well, that's harder to explain, but it also has to do with filters in the brain. When I walk down the street and see a group of people standing around and say they start laughing, I may unconsciously think for a second that they are laughing at me. But as soon as the thought comes into my head, I brush it off and move on. A schizophrenic does not have that ability to brush it off. They would continue to entertain the thought that those people are laughing at them.
Ever have a moment in your life where you thought that maybe someone was out to get you? Or maybe your walking through a dark alley at night and feel like someone is watching you? For the most part, you realize it is just silly, but you may create and elaborate fantasy of some dark stalker out to get you. Even as you create this fantasy on your head, you know it is not real. If you don't have schizophrenia, you brush it off and realize its just silly. A schizophrenic feels those eyes on their back and runs with it. They go with that fantasy and as they are having it, it becomes a reality.
As you can see, schizophrenia is a result of what some psychiatrists in my field refer to unprofessionally as fuck-think. Its not about brain damage or a viral infection or loss of oxygen. It is a result of distorted thinking. While some forms of brain damage can result in distorted thinking, nothing comes close to mimicking schizophrenia.
Excessive use of some psychedelic drugs can cause schizophrenia, but experts speculate that when someone becomes schizophrenic from the use of drugs, then they probably already had a genetic predisposition towards it. The drugs just exacerbated it and brought it to the surface.
I know people who have done vast amounts of LSD, Mushrooms, DMT, Peyote, Meth, robo trips, etc... the lost goes on and on. Yet they are for the most part, psychologically healthy people, fully capable of functioning in normal society. Other people can take one hit of acid and well, never come down. These people had perfectly healthy upbringings with good loving and attentive parents, yet, they were always a little weird.