Some people who want to keep cannabis illegal claim they are reducing harm - reducing harm to users, to those users' families, and to wider society.
I think there might be causal links between cannabis and mental health problems. And there are a bunch of self-medication and masking problems too. But even though I believe this I cannot understand how people do not see the much worse harm that prohibition causes.
In England there is a problem with criminal gangs using trafficked workers, keeping those people imprisoned in houses which are then turned into cannabis farms. If Bob wants to use cannabis it is more sensible for him to buy it from a criminal gang than to grow a few small plants purely for personal use because the crime he commits by growing it is much more serious.
Reading about the situation in Mexico is horrific.
> In Mexico relatively few people take drugs. But many are murdered as a result of the export business. About 60,000 have been killed by organised crime during the past six years.
Sixty thousand? That's a mind-boggling amount. (There's a tv programme in the UK at the moment about road safety, with lots of "how do we reduce road deaths?" About 2,000 people die each year in RTAs in the UK.)
Even stupid people should know there's a serious problem when they're told there is a criminal called "the Soupmaker" who dissolves victims in vats of sodium hydroxide.
(http://www.economist.com/blogs/americasview/2010/09/mexicos_...)
> another collaborator of Sinaloa's, Teodoro García, was captured in the coastal city of La Paz. He was accused of ordering his victims to be dissolved in barrels of acid by his henchman, known as “the soup-maker”.