Your first argument is the same argument used every time new technology comes out. Friction shifting? Why do I need friction shifting? I can change gears by turning a lever on my seat stay. Indexed shifting? Why do I need indexed shifting? I can change gears by turning a lever on my down tube. Electronic shifting? Why do I need electronic shifting? I can gears by turning a lever on my brakes. Automatic shifting? Why do I need automatic shifting? I can shift gears by pressing a button.
After setting up a computer for different types of rides based on power output, heart rate and any other inputs there may be, and then you need only to choose 1 before the start of your ride. Seems to me it would be an excellent tool for training.
I guess that works if you ride the same throughout the entire ride....I don't generally do that. I switch it up all too often depending on how I feel at that moment, not how I feel at the beginning of a ride.
I just think there are too many variables, namely the "engine" not being static like an automobile, for automatic transmissions on a bike to be of much help. This is entirely different to the clear advantage indexed shifting has over friction or downtube vs. brifters. I question the advantage not because of some luddite-type hold on the past, but I just don't see it working well with a human. Also, if they incorporate some way of switching based on what the rider wants to do at that moment...like you switch a button to go into "stand up mode" I don't see that being all different than just using regular old gear shifters....so question the point. Adding complexity for nothing.
BTW, I love the idea of electronic shifting.