Banning all carry-on luggage would destroy the airlines financially. No way I travel on business as much as I do if it requires checking luggage all the time. I had to check my luggage last month when I was on business for a week, and it was awful.
Many other business travelers feel the same. I need to get in and out of the airport - not stand around a luggage carousel with 48 screaming 3-year olds waiting on the 80% chance my bag actually arrived. And I certainly don't need my laptop sitting on the tarmac in a driving rainstorm, waiting to get tossed into the luggage compartment by a $7/hour nitwit.
Can you imagine all the junk folks would claim as medical essentials? Hide something in pill bottles or even in what looks like factory made foil wrappers. Then there's the diabetes equipment. I have one of those metal thingies that you put a seringe in so you don't see it poke you which would make a great gadget. A few hypos filled with the right thing could disable flight attendants and pilots. Wheelchairs, casts, artifical whatevers, etc. all should be banned. I'm only half joking but it's to the point they should make everyone fly nekid! But then there's the question of the cleaning crew or maintenance or surface to air missiles...