I wonder if you feel the same way with someone who queues for McDonalds and orders a BigMac, then changes their mind and orders a Chicken Sandwich, do you feel they should go to the back of the queue or be allowed to change their order whilst maintaining their queue position?
Think of it more as 2 separate queues, one for Big Mac, one for McChicken, you wait ages in the big mac queue, then you see the McChicken queue is going down faster, so you jump across and barge in front of a guy with his mouth watering for a McChicken who has waited as long as you, and push him back.
Sad thing is, you didn't even really want a McChicken, when he had his eyes on one all along.