Normally I'm opposed to all kind of mind-altering drug use, I don't even drink alcohol myself, neither do my immediate family members.
But I do agree with you, that cannabis should be legalized everywhere, partly because of the health benefits you mentioned, partly because of its effects on the legal system and on the economic system.
Those who grow and sell cannabis products would no longer be connected with those who produce and sell harder drugs. Far fewer people would have to be prosecuted and go to jail.
And hemp the plant from which cannabis is made has a lot of beneficial commercial potential. It could partially replace cotton in cloth production and wood in paper production, while growing much faster than wood and in more climatic zones than cotton. And so it would have environmental benefits as well, reducing the need for cutting down trees.