You're seriously overestimating the willpower of modern humans. Humans always take the easy choice, when possible.
There's some truth to that, but the point is there's always a choice to be made. Almost all druggies started out by making the choice to use drugs. No one forced them to smoke this or that or stick needles in their arms or gobble pills.
Why should people who make the right choices in life be on the financial, social, and psychological hook for people who CHOOSE to put drugs in their bodies? People shriek and moan and b*tch about the idiots who CHOOSE to hike into the mountains unprepared and then rescue services are called in to save them. Druggies are VASTLY more costly to the taxpayer in innumerable ways.
Druggies are a plague and the cure is looooooooong prison sentences or death or they lose their citizenship and are permanently booted out of the country.