"...think of all the damage that would be done to the Pharmacutical and liquor industies if it were legalized "
When it comes to the American government, it's always follow the money. Always. You make a good point, but there are 2 more problems: #1 - The stuff would grow on concrete. It would be almost impossible to generate enough revenue if it were legal. Anyone could just grow what they wanted. #2 - There is no shortage of constituents that want to run other people's lives. Even if the only person you harm by smoking the stuff is yourself, there will be people lying awake at night trying to figure out how to stop you. Votes translate to money.
Oddly, some of them claim to be "conservatives."
I'm sure you realize that my post was typed ... tongue in cheek ...
" Anyone could just grow what they wanted"
You could say that now about fruits & veggies, but most folks choose to buy our produce from others.