2. I completely agree with you but do you think that legalising it is going to reduce the health impact? No, it's going to make it socially acceptable.
Shit or get off the pot: Cite your sources regarding addiction.
Edit: Ask for proof/sources = down vote. Hey everyone, fuck science.
America showed the hell that can come from alcohol prohibition. Only an idiot would look at that and consider it a solution to some anti-social behavior on the weekends.
2. I'm not sure it will make it socially acceptable. From what I've seen in the Netherlands a lot of young people think it's 'uncool' to smoke marijuana. And regarding the health impact if it is legal the government will be able to put out advice on minimizing the health consequences (e.g. using edibles, not mixing with tobacco, vaporizing instead of smoking etc.).
As for sources - Google it. I did and found several sources in seconds. The sources vary on specificity but the general message is people can become dependent but that it isn't very addictive.
1. The person that crashed into you (sorry, that sucks) could have done the same thing after drinking alcohol. It's legal. Do you also recommend prohibiting it? I think most people would agree driving under the influence of marijuana should be illegal. Punishments should be severe. But even now with prohibition that doesn't stop stupid people doing stupid things. Illegal or not, the world is full of idiots and there's very little we can do about it.
2. I don't mean to be insensitive but your sister-in-law made that decision. It's her right. You have no right to enforce your views on her. I have seen many people addicted to alcohol and it's horrible. But they have an excuse - it's highly addictive. Marijuana isn't. It is less addictive than caffeine meaning that if she is choosing to spend her days on the couch, high, it's a choice she's making.