I think that tended to be the bipolars, not the schizophrenics, but fair point: what is or isn't "sick" has changed throughout history.
This actually brings up an interesting point about schizophrenia: it
varies by culture! In "Western" culture (presumably this is true of the OP, in Germany), the voices heard tend to be more violent, hateful, and are generally perceived as negative.
However, in India or Ghana schizophrenics actually perceive their voices positively. Obviously the biology is the same in both, so it seems wild to me that you could have a lifetime of asshole voices in your head, or a lifetime of friendly ones, just depending on where you grew up.