If weed were fully legal it would be quite ubiquitous. It's a hardy and prolific plant, and if people threw seeds around, it could grow wild throughout most of North America. People might grow their favorite strains in their backyard gardens, much in the same way they grow tomatoes today, and trade clones to keep it fresh. I could see a problem with growing it outdoors as neighborhood kids may hop your fence to pick a few choice buds, but then we could grow it indoors without hiding it, similar to the way folks currently brew their own beer in their homes...