Standing ahead of me in line at Open Pantry were a guy and his two or three little kids, each of whom got a handful of candy. He asked for a separate plastic bag for each child's candy and was given one. That should be simply illegal, or at least heavily taxed. The cashier should have had to say in response, "That'll be a dollar for each bag, please". This is simply one of those areas where the government is going to have to exert behavior modification, as it has done with tobacco control.
If you could not care less about the environment, consider that you have to pay for the cost of trucking the plastic bags on their way to Open Pantry and from wherever they are thrown out.
Still, I reserve the majority of my scorn for the customer for just being an out-and-out dickhead.