I agree, it could be proportional, but I see no easy way how to implement that. My notion is that if you consume harmful products "in moderation" or as you say responsively, then the amount of your purchases is already small enough that even a high price won't cost you a fortune (in total). It is exactly the price that will drive down the consumption to a harmless level. That is the sweet spot that needs to be found.

My fears are more in direction of bootlegging and other ways people find to circumnavigate this policy.