I'm going to try and clear a few things up here. People are speculating without sources.
These two links are related to Marijuana use and how they impair driving skills:
http://www.sciencedaily.com/releases/1999/03/990325110700.htm Short link
http://norml.org/index.cfm?Group_ID=7459 This is a longer study with plenty of other interesting articles on the site.
Those who have smoked Marijuana and decide to drive are a lot more careful about what they are doing. The paranoia that you get makes you more cautious, it certainly makes me more cautious. Although they are impaired by the drug, they are aware of it and seek to compensate by being aware of this. I couldn't find any graphs, there aren't many tests carried out on illicit substances, which is quite silly.
97% of drug related deaths are from legal drugs, according to this source:
http://newsrogue.com/97-of-drug-deaths-from-legal-drugs/.
The majority of deaths caused by illegal drugs are due to impurities in the drug - if you are used to street quality heroin and you shoot up, your usual amount, with some high-grade stuff you are going to die.If the government controlled drugs then there would be a standard purity, this would reduce the percentage of deaths caused by the substances.
People are also killed over, large scale, drug deals because the market is in the hands of criminals.
I hope people will take this into account before making ill-informed statements and claiming them as facts without proof. At least give sources if you are going to make claims. To finish off, people aren't likely to, purposely, lace marijuana with other drugs because it's a waste of money. People don't pay extra for laced weed, the dealer would be throwing his money away. Dealers aren't stupid, for the most part, they are business men.