If my neighbour is drinking alcohol it doesn't fill my flat with rancid smoke. If my neighbour is drinking alcohol it doesn't magically pour down my children's throats while they sleep.
Have you ever taught a child who stinks of cannabis? I have, many times. I've never taught a child who stinks of their parents' alcohol.
Millions, if not billions, of people manage to drink alcohol without becoming violent (myself, and everyone I know, included).
My cousin ended up being commited due to cannabis related psychosis. Like all substances ingested by humans, it has wildly differing effects on different people. Like all substances, people use it inappropriately - a colleague of mine was hit by a drug-driver.
Are you suggesting that alcohol should be made illegal? Or cannabis legalised? Or both? Either way, a minority would do stupid things whilst under the influence of either substance.