There is a simple solution.
Airlines use fuel to fly their aircraft. The heavier the aircraft, the more fuel is required.
My wife and I are both smaller in stature, weigh less than most other people, and we are usually pretty efficient in our packing. The two of us, with baggage probably weigh less than some individuals alone.
I think when you fly you should have a minimum seat rental fee plus a weight cost. Therefore, my wife and I would pay a fee for the space we occupy, 2 seats (and I mean 2 seats without a large person encroaching on our armrests just because they see we have extra space), plus a fee for our body weight and baggage combined. So, if we weighed 310 pounds with baggage, we would pay the same weight cost as a single larger person, or a single person with heavy bags.
To my tall or big friends, I understand things may not be all that comfortable for you when I recline my seat, or put my bony elbow on my armrest, but I didn't make you tall or big, and it is not fair for you to encroach on the space I am using just because I'm smaller than you.
As for the seat sizes and room on a plane, you can buy a first class ticket if you want more space or suffer with the rest of us.
I have a hard time having sympathy for KS, or other large/tall people. I can't tell you how many times I've ended up squished against the window because the person in the center and on the isle are both large, and they act like they are entitled to use as much of my space as they want.
I heard someone suggest putting panels between the seats instead of merely armrests. I'd love the opportunity to request one of those. I have plenty of room unless someone next to me tries to take it.
I wouldn't be worried. Ultimately, the final decision on whether or not to fly is the pilot's, not ground crew or a bean counter at the corporate HQ. The pilots have families they want to get home to too, so if they feel the plane is unsafe to fly, they will not fly it.
Actually, there is an office on site at each airport for each airline that is responsible for weight and balance of the aircraft. That office relays the information to the pilot who then has to make sure the changes required are made.