While it might be comforting to believe this, there's strong evidence that while directly killing alcoholics was not the goal, it was a known and acceptable collateral damage. Even after being confronted with the unprecedented number of deaths, the official response from Wayne Wheeler (the leader of the Anti-Saloon League and generally acknowledged architect of Prohibition) was that "The government is under no obligation to furnish people with alcohol that is drinkable when the Constitution prohibits it. The person who drinks this industrial alcohol is a deliberate suicide."
https://books.google.com/books?id=8gAtAgAAQBAJ&pg=PT173&dq=%...
Edit: Here's a political cartoon from 1927 attacking Wheeler for the deliberateness of his approach: http://archive.lib.msu.edu/DMC/tribune/trib00000000/trib0000...
The goal was never to kill alcoholics, but to prevent them from stealing industrial alcohol. I think the people behind it didn't think anyone would be stupid enough to try to drink or sell this stuff.