Jerry Seinfeld had a rant about why he felt justified leaving his trash behind in the theater...he paid $7.50 (it's an old routine :-) ) for his ticket, the theater was making enough money, let them clean it up.
Except of course he wasn't hurting the theater owner one tiny bit, just adding one more little bit of aggravation to the lives of the minimum wage employees who have to clean up after his lazy, entitled millionaire butt.
If I drop the stuff, by mistake, then yeah, that is what the employees are paid for, though I feel pretty crummy that I've made their jobs harder. If I throw the stuff on the floor, or even LEAVE it there intentionally, I'm jist being a jerk.
I don't see how leaving an empty popcorn bag on the floor of a theatre is making someone's job harder. Their job is to clean up. I could see how stepping on popcorn and grinding it into the carpet, or spilling soda, or leaving it wedged in your seat, could be an issue. In fact, if everyone took their trash with them and was perfectly clean, there would be people losing their jobs because there would be nothing to clean up.
Or I could be busy making sure that people aren't sneaking into theaters or being rude, that the projectors are running the right way, that the bathrooms are clean, that the tile slick with butter is being mopped, and that the trash bags are put into the dumpster and replaced (I or my coworker did all of that last night). I sure wouldn't lose a job if people picked up their drinks and bags and put them in the trash can the ushers put out for their convenience, but it would help me to do it faster and more efficiently.
I promise, when there's a rush to get 10 auditoriums clean in 30 minutes, it makes it infinitely easier if people try the best they can to keep their area clean. I don't expect spotless floors, because popcorn can go everywhere, but not walking (general) your concessions out to the trash can just because I can do it for (general) you is, frankly, entitled and really Special Snowflake.