See a doctor before smoking weed? PMSL! :D I don't think many will follow that bit of advice.
Interesting post, all the same. Re mental illness - I'm coming to be of the opinion that mental illness is one long continuum. Everyone has it (or at least has had it) to a degree, I'd say. Whilst government agents will say weed leads to mental health issues, I'd say governments cause more!
Maybe it could exacerbate a serious condition (eg. schizophrenia / depression, even) but then again they're happy to take bribes off breweries and allow alcohol to remain legal which has to be considerably more dangerous to just about anyone who drinks (and people affected by people that drink).
There are a million and one worse things legal. But that's governments for you.
RE: Cons of cannabis