This too is absurd. If that line of thought were followed, restricting things would be restricted, as would everything else. Also, Devlin has a bad habit of exaggerating beyond the bounds of reality in an attempt to prove his point. Of course society would collapse. The aspect of this argument that Devlin overlooks, of course, is that if there were a society of people who actually would get drunk every night, society would collapse regardless of whether someone tried to restrict liquor or not.
Society is made of people, and if the people are bad, then society is bad.
One cannot try to keep society pure when all of its people are not. It is a logical impossibility. Another strange aspect of Devlin's book is his total lack of respect for, and trust in, the average member of his ideal society. And even worse, in the above quote, Devlin was speaking of ninety virtuous and ten who practice vice. It must at least be considered possible that some of those who practice vice would become virtuous.