IMO the airport is the one who is responsible for dealing with the trash. If they want to recycle it, and make the airline sort the trash for them, fine. If they're lazy and just dump it in the landfill, fine but don't blame the airline for using plastic cups.

What should be mentioned is that when flying, the risk of getting an illness from someone else on the plane is much greater than normal. Diseases can spread around the world in a day because of air travel.

I've seen FAs use gloves when collecting the trash before landing. There is no way I would want the same treatment to my cup with a refill -- that's almost like eating out of the trash.

There is one way you could reduce the number of plastic cups to nothing -- serve coffee or tea in a styrofoam cup, and everything else in the aluminum can it comes in, stored cold. No ice, too bad. If you want a Jack & Coke, take a few sips out of the Coke can, then pour the mini into the Coke can and now you have a mixed drink in an aluminum can (again, no ice, too bad). Aluminum can be recycled much more easily than plastic, so that's another advantage. Personally I could deal with that but a lot of people insist on ice. Also the airline has to give you a full can of soda instead of just a half which fits in the small airline size plastic cup.