If your justification for legalization is that people will do drugs at home, but you concede (correctly) that they won't .... well, you lost me there.
I REPEAT my question - what is the problem for those adults who drink/get high/whatever else - responsibly - & don't pose a danger to other people? You say if pot is legalized you know for a fact that twice as many teenagers will smoke it? Could you show me facts on that?