Hmm well let's see if it were made legal it would be grown outside in fields, each plant if genetically engineered and under the good yellow sun would grow at least half a pound (it would probably be more but whatever, currently you can get around a pound outside if you know what you are doing and with certain strains.) It really would take almost no land at all compared to land available to produce this due to the small amount consumed to get high. Prices would plummet to incredibly low levels. Secondly 50,000 people died in the last five years in drug violence on the Mexican border over the illegal drug trade. Make it legal and then this violence gets reported to police thus dramtically lowering it if not causing it to vanish (Mexico already has decriminilized small amounts and is talking of legalization but won't due to U.S. pressure). Secondly due to price plummets gangs will not get into the drug trade because it will not be profitable thus no drug gang violence. Furthermore every country that has decriminalized to some extent has seen lowering in drug use (Portugal, Amsterdam, Switzerland), So if lowering drug use, saving tens of thousands of lives and stopping the imprisonment of tens of thousands of people doesn't seem like solving anything to you then you should really stop breathing.

Also, a lot of weed here in Scotland (and probably the UK) is dipped in chemicals to make it look more crystallised so people think its better weed. Often it is pesticides or other very harmful chemicals that are used which can't be good for you when you smoke them.