Is it really worth locking up a million people to have 300,000 less heroin addicts? Even if you suppose the War On Drugs IS working (and it seems like it is NOT to me!) that doesn't necessarily equate to the human cost being worth it. Drugs can ruin lives, that is certain, but so can prison sentences, it makes a lot more sense to treat drug abuse as a medical issue than it does to treat it like a criminal justice issue. It is a failure in logic to say, "drugs ruin lives, so if we catch you taking them we will ruin your life any way by locking you up!"
Why is it relevant how many chemicals are in marijuana smoke, when several of them have been shown to have a medicinal benefit? If many of those chemicals are potentially beneficial then it is misleading to present the fact it has 468 chemicals in it as a bad thing. It also doesn't seem very relevant to claim it has 60% more carcinogens than tobacco smoke, without mentioning the fact that there has never been a case of cancer that can be solely attributed to cannabis use, where there are thousands that can be attributed to tobacco use. There is a tiny chance I am wrong on that last part, but I am fairly certain I am not. Regardless, several of the chemicals in cannabis have been shown to help fight cancer, which clearly offsets at least some of the carcinogen consumption.
I also think you missed Poledrivers point earlier pmoseman, his point was that cannabis is NOT more carcinogenic than tobacco smoke when it is used by means other than smoking, like vaporising and taking it orally. Considering that these are both perfectly viable means of ingesting cannabis the argument for banning it based on the health consequences of just one possible route of administration is pretty thin.