I think calling cannabis bad or good is a false dichotomy. Sometimes peanuts kill children, that doesn't make peanuts "bad". Maybe cannabis causes schizophrenia in rare cases, does that make it "bad"?

In this specific case, the authors started him on a treatment for schizophrenia and he got better. Why continue him on this treatment if they thought it was simply the cannabis that caused it (as he would abstain from then on). Also, they increased his dose prior to discharge.

I'm not arguing that cannabis didn't cause his schizophrenia, just that this doesn't sound like cannabis induced psychosis, which is a different diagnosis with different prognosis.