I do not know the formal definitions for what you are doing, but your thinking is A$$-backwards. Your conclusion is that Pot is the devil, and you assassinate logic in your attempt to prove it.
" Not all people who drank milk or beer become hard drug users."
True, now you're suppposed to ask yourself:
'Do all people who smoke Pot become hard drug users?' No they do not. Pot is similiar to beer and milk is that respect. But instead you jump to:
"...nearly 100% of hard drug users smoked pot before moving to the hard stuff."
Yes, but they also drank beer & milk before 'moving on to the hard stuff'!