1. There is no evidence anywhere that smoking cannabis causes cancer. None, zilch, nada.
2. Gateway is a myth. Evidence demonstrates the first drug tried by most addicts is by far alcohol, with prescription pain killers close behind. Cannabis does not even register.
3. There is no evidence anywhere than cannabis consumption alone leads to traffic accidents. In fact, there is some that directly disputes that notion.
4. You are half right about the black market, Trudeau's notion that cultivation should be controlled by the federal government licensing only a few producers will result in a continued involvement of the black market.