Here's the link again, I suggest you read the abstract and conclusion, if not the whole thing. It discusses everything I've been saying, and it's from 2008.
Psychological events related to cannabis use: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2424288/#!po=0.980392
English
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There is increasing evidence that the association is biologically plausible, but given the complex nature of the aetiology of schizophrenia and related disorders, it is unlikely that the relationship will be due to an interaction between cannabis use and a single gene. They sure do sound sure of themselves don't they. Taken from the conclusion of the link you provided