Weed is far less dangerous than smoking. Not saying it's a good thing, but you can't get physically addicted to weed itself, only to the nicotine you usually put in the joints. Meaning, it's far easier to get away from weed than is it from cigarrettes.
And in order to overdose on weed, you'd need to consume around 20 kilogram - an amount that would be probably be impossible since you'd throw up all over the place before even coming close to it. Even then you're very unlikely to die.
If you truly think weed gives you cancer, you're an enormous idiot, because the mixture in cigarrettes is the main reason for helping the cancer develop, not the smoke on its own.
Seriously, arguing that weed is worse than nicotine is stupid; you get addicted to nicotine easier, are more likely ot get cancer, don't even get an instant benefit out of it, and so on.
The reason why most smokers are unhappy is because most people start smoking due to a huge amount of stress/depression.