Legalization changes that because it makes it a lot easier to cultivate in the US, safely and legally. Illegality encourages actions like smuggling from Central and South America, and guerrilla grows in National Forests. With decreased legal pressure, more savory elements of society produce high quality cannabis in the US. So, even if that produce is sold on the black market its a better situation than violent gangs from Mexico smuggling bricks of marijuana with theI meth, cocaine and heroin.