The central thesis of the Selfish Gene has nothing to do with "junk DNA", and when the book does talk about the subject it doesn't assume that it has no purpose

The central thesis of the Selfish Gene has nothing to do with "junk DNA", and when the book does talk about the subject it doesn't assume that it has no purpose. (What it does say is "Biologists are racking their brains trying to think what useful task this apparently surplus DNA is doing" and "The simplest way to explain the surplus DNA is to suppose that it is a parasite, or at best a harmless but useless passenger".)