It would be nearly impossible to "inhale" enough marijuana smoke by way of a smell coming through the floorboards to affect a human being, even a child. Add to that the fact that marijuana is pretty much totally non-toxic, and that pretty much kills your first point. You'd have more success trying to convince people that a ban on internal combustion in public places should be outlawed as it forces people to inhale noxious gasoline fumes.And what good would be accomplished by this, pray tell?Call and have them arrested. It's the right thing to do.
Perhaps prevent children from inhaling drugs? Perhaps prevent other adults from inhaling drugs who may not be drug users themselves. And it would be the responsible, adult thing to do.
There would be nothing responsible or adult about it. The responsible adult thing to do would be to have a polite talk with them, not sick the gestapo on their tail. The laws banning the use and possession of marijuana are archaic and need to be done away with, especially since far more harmful drugs are sold legally every day - alcohol, tobacco, prescription pills, you name it. Being a law-abiding citizen is generally a good thing, but you need to think about the laws and the merit they have on a case-to-case basis, not just obey universally with slavish subservience and rat out all who do not.