I would review supply and demand. The demand most likely would not change. Pot being 'mass produced' vastly increases the supply. Prices would plummet.
Supply issues aren’t really what keeps marijuana so expensive in the black market. Other factors cause that. It starts with high production costs. Modern farms producing legal agricultural products tend to be in the thousands of acres. Small farms with a few hundred acres can’t compete with the large farms even though the small farms tend to be using modern agricultural methods. Pot farms are rarely ever in the hundreds of acres. Most plots don't even cover a whole acre, and the marijuana farmer is not using machines to plant his seeds and combines to harvest and machines to process his crops. He’s hiking out into the boonies to plant and tend to his tiny little plots, doing all of the work by hand. It’s even that way in Mexico where they used to get away with growing huge fields of the stuff, and all of these growers and the people that help them are demanding super high pay relative to what others producing legal crops produce because they are taking huge risks.
Thousands and thousands of tons of marijuana are produced in North America every year, mostly in small plots, and increasingly indoors where growing space is measured in square feet, not in thousands of acres, and where growing costs are incredibly high because they have to use artificial light to produce their crops.
A lot of marijuana is seized by law enforcement before growers can harvest it, and a lot more is seized along the way before reaching the end consumer. Smuggling it across the border is incredibly expensive. A truck driver with a couple of tons stashed in his legal load might charge fifty grand to drive that load across the border. Often big bribes end up getting paid to border guards and customs officials, etc. Then they have to pay to get it transported to safe houses, and will pay thousands to people who take comparatively small loads of a couple of hundred pounds in the trunks of their cars across the country to other destinations. It’s expensive as heck to produce, and really expensive to transport and distribute. The product changes hands so many times and everyone who touches it wants to be paid handsomely for the risks they are taking.
If it was legal and produced on a huge scale like other crops are produced today, most of these costs would shrink down to a tiny fraction of what they are today. It would be a whole lot cheaper to produce, transport and distribute. It would change hands far fewer times and those involved in producing and distributing would not command nearly the premium they command today because the risks would be gone. They’d make their money by moving a large volume of product, profit margins would be much thinner but they’d make up for it in volume. One licensed retail shop would do the work of perhaps hundreds of little small time pot dealers. A truck driver with a 90 thousand pound load of pot would get paid about what the guy with a couple of hundred pounds in his trunk gets paid today, or actually probably considerably less. Costs would plummet.
I don’t know that we’d see a huge increase in supply though, because like you I doubt demand would increase that much. I think most people who want to smoke marijuana already smoke it. I’m sure there are probably a few people out there who have no other reason for not smoking it other than the laws against it, but I think the overwhelming majority of us that don’t smoke it don’t smoke it because of all the other reasons it’s a bad idea to smoke pot. Making it legal would not take away all those other negatives.
Oh please. The number of users would double, if not triple. Teens, especially.
Marijuana use was as low as 4.6% in the 90's and as high as 13.2% in the late 70's. Legalize it and we could see the number rise to 15% easily. Especially if it's going to be as cheap as everyone says.