EDIT: Make it clearer by saying "Pepsi (absolutely not Coke or any other brand)" by all means but the person buying the drink wants to make sure you get what you want and then get on with their lives, they're really not interested in the why.
It feels to me that Stallman wants to use this - as with most of what he does - as something of a polemic about what he believes. That's fine but it does make the whole document less clear about the actual detail of what he wants.