While I do believe that it could be legalised and sold in a similar way to alcohol, I think it is misleading to suggest it is a potential treatment for depression. My mother suffered from a variety of mental health issues, and cannabis absolutely increased her depression and particularly paranoid delusions. It was plain to see the negative impact the drug can have.
The way I look at drugs is like any other choice in life - go ahead and do it, but educate yourself first and understand the risks.