Here are some bullet points and factoids:
-the difference between a drunk driver and a stoned driver is that the former will run a stop sign. The latter, however, will simply wait for it to turn green.
But seriously:
-It's nowhere near as unhealthy for you as cigarettes (~20 cigarettes a day versus 1-4 joints) or alcohol (long term liver damage).
-There are no physically addictive properties, unlike (you guessed it) cigarettes and alcohol.
-It isn't possible to overdose as a result of smoking, eating, or vaporizing cannabis.
So, as far as health and safety goes, this plant pales in comparison to legal alternatives.
Why I support decriminalization instead of legalization:
-I don't believe in the regulation of psychoactive substances. It invites taxation and an overall diminishment of the final product.
-Decriminalization solves the number one problem of cannabis users: it keeps them out of jail. Therefore, the government involvement is minimalized. It also severely lessens the penalties for unlicensed growers and dealers. Nobody deserves jailtime over something so common and harmless.
-Legalization would put a lot of dealers and growers out of business (due to loss in sales and the taxation) and leave smokers with a more expensive and lower quality product.
/soapbox
/roll