As far as the links to schitzophrenia... eh. Show me the schitzoids. I've known smokers who have smoked (probably daily) for at least 40 years and are hardly schitzophrenic. In fact I don't know 1 smoker who ever developed schitzophrenia. Yeah, that's not very scientific and I think maybe if someone has a propensity for schitzophrenia and then uses drugs that problem is going to be made worse, like it would for almost any drug. As far as I can tell though this is such a small, small minority but it serves to frighten. It does sadden me that legalization has used medical marijauna as a fig leaf. It's Orwellian word games. On the other hand those who take lots of perscription "medicines" are often fooling themselves too about why they need their "medicine".
Some specific brain pathways are implicated in marijuana use in relation to the development of schizophrenia. Note that marijuana is not going to cause schizophrenia in individuals who don't carry any of the schizophrenia genes. I think that the only definitive answer is to set up a study in which the marijuana usage habits are compared between sets of individuals who carry the gene mutations normally associated with schizophrenia, and to determine if more of the marijuana users become schizophrenic than those who don't.
In my whole life, I have only known two schizophrenics; it is not a common disorder.