I thought the conversation was about weed.
"Weed" is like Gay Marriage. You let them succeed in that, then pretty soon you will be forced to bake gay wedding cakes.
"Weed" is the camel's nose in the tent. All arguments which are currently being trotted out to justify weed, justify all other substances as well. You let them have weed, and you won't be able to stop them from having Heroin.
"Weed" is just always the innocuous opening move in this larger struggle between the forces of darkness and the forces of civilization.