What kind of human goes their whole life without trying a drink or smoking some weed at some point? and it's not just drugs, you could get addicted to a lot of things (gambling, etc)
They've done studies with identical twins dude, 50% of addiction is caused by a genetic predisposition (other 50% is due to poor coping mechanisms). The children of addicts are 8 times more likely to become addicts themselves.
so it's not the vice, it's the ease of addiction to it.
When do they ever do that? 
