I think it should go only by weight. There would be scales at the check in so people could not lie. The airlines set a maximum weight like for instance 170 lbs. If you exceed that you have to buy two tickets and have two seats. Period. Or you do not fly. I mean I’m overweight myself but I know it is only fair to other passengers and safe for the airlines. It would just be a regular fact and not anything personal so I can’t see getting upset about it because big is big and it's not like they are revealing a secret. As I said in a previous post, here I thought that was already the standard policy. But I can tell by all these comments to the contrary I thought wrong. Guess it shows I have not had an occasion to fly in years.
I think going by weight is a pretty bad idea. I am 6’3” and about 220 pounds, I need to lose about 10 pounds but I am not considered obese. I don’t see why I should have to pay more because I was not born a 90 pound woman. Now if I was like 300 pounds and took up more than one seat I could see charging for two seat. The airlines could be a little more considerate. Since I usually fly on the Navy’s dollar, upgrading isn’t always an option but I have had a few places mainly Delta who has been good about getting me a seat with a few extra inches for my legs.
As for charging by luggage and passenger weight, that could be bad and good. When I take my seabag with all my uniforms, the bag weighs dang near 75 pounds. My friend with the same amount of uniforms weighs about 10 pounds less because he is a little over 5 feet tall. 170 pounds is definatly not enough weight. I have worked my butt off to drop almost 20 pounds and guess what, I still take up the same amount of space and I am not considered obese.