Seat stays are load bearing. They bear compression. They bear the entire weight supported by the rear wheel, which is 60% of the total weight.
All parts of the frame bear load. If there was any part of the frame that wasn't necessary, it would have been eliminated to save weight.
Watch this:
Talk with someone like Rob English.
Seat stays are in place because the UCI dictates what makes a bike frame.
Fixing carbon is easy. Roadies are failing to learn things that mountain bikers learned years ago.
Road bikes design is dictated by the UCI and racing rules - which is the reason why the whole "aero" bike thing is a joke. Lipstick on a pig.