I don't know if you have been addicted to something before?, but if have you would understand how difficult it is for the people that smoke marijuana to abstain from it.
You know, to them it's just something that makes them feel good,happy, and some people would say it inspires them, so when you talk about the health implications they don't seem to be interested because they can't do without it, some might want to stop but can't
That's the level of damage it has caused to human race and the world at large