Have a read of The Guardian's special report on suburban cannabis cultivation. It makes interesting reading, though not for the fact that lots of people are growing weed. 
We know that lots of people smoke, and the supply has to come from somewhere. The government, through making cannabis a black-market product, has made cannabis users in to unwitting supporters of criminal gangs, like the Vietnamese people smugglers the article describes.
But this bit stands out:
Police are concerned that British-produced cannabis contains more THC - the psychoactive component in cannabis - than foreign imports. Analysis of recent homegrown hauls detected THC levels as high as 20%, nearly seven times higher than samples of imported resin, which used to be the predominant form of the drug on the streets, and typically contain around 3% THC. Experts fear this could have health implications for the country's 2 million regular cannabis users.
Yes, cannabis with more THC has an important health implication for cannabis users - you don't need to smoke as much weed to get high. In a country that's obsessed with the health of smokers, increasingly high THC counts should be welcomed as a good thing - as it means that cannabis users don't need to smoke so much.
The health implications of a higher THC count are primarily good. This has been backed up by evidence in the United States, as described over on Wikipedia where use of low-potency marijuana presents a cause of "abnormally high blood carboxyhemoglobin levels" and use of higher potency weed is pointed to, along with vaporisers, as a method for reducing the harm done by smoking.
It also means that cannabis users don't have to buy so much weed to get high, meaning less money is going to the criminal gangs that are running the business because of the continued criminalisation of cannabis in Britain.
Later in the article, they describe how grow-ops emit a large amount of heat and pose a fire risk. Well, if you legalised it, ordinary people would be growing it along with their tomatoes and rhubarb and it wouldn't be a problem. It would have the health risk equal to - I don't know - showering or eating a bowl of corn flakes or something.
It's saddening that the Guardian put this story together without any voice for the liberal/libertarian folks - like me - who want to see an end to this ridiculous war on drugs, from which only drug dealers are winning. The enormous amount of good that cannabis does - both in terms of medical marijuana use and in terms of making people happy and contented is always overshadowed in the media by scare stories of the extremely rare cases of people who suffer from psychotic/schizophrenic episodes triggered by marijuana.
We now have the minor disadvantage of being unfashionable. We have the major advantage of being right - Amsterdam isn't a chaotic hell-hole, it's the rest of the world - where paternalistic prohibition policies are in place - that's got the drugs problem. The harm done by cannabis is outweighed many times over by the harm done by the laws against it's use and production.
