Wow, I didn't know you guys were all that "healthy", weight wise! I hope I didn't offend anybody.
I myself don't care about remarks like that and there has been more than one occasion where I was called a "skinny little s#!t" and even got in trouble where I found myself defending myself against "bigger kids" who thought they picked an easy target. But such is life.
For example, you guys couldn't work for my day-job as helicopter pilot either. We have a 200lbs limit for our pilots. Discrimination? --> not really. Our contracts are all bid using a "standard" pilot weight of 200lbs, and the performance margins are really close in light helicopters, so if we had a 300lb pilot show up, the USFS would unofficially frown upon that. Officially they couldn't do anything because they are more afaraid of getting sued than anybody, but still we wouldn't wanna be in that situation. Not to mention it's a safety thing for us as well. The CG limits on those ships are reached a lot quicker on a helicopter than on an airliner. And then there is a lot of physical work as well (hauling gear, water bucket, and so on) and that at 8000ft and above....
When I was flying offshore, we were using a "standard" weight of 220lbs per passenger per manual. But we ended up adjusting that ourselves up to 260lbs per pax because oil field workers are BIG GUYS!

Not fat and/or out of shape, just really really huge guys. I never felt as small and short than on an oilrig!

I actually ended up finding the gym on every platform and worked out like crazy while I was waiting for my pax trying to bulk up. (got me in shape but my frame just isn't built to get all yolked

)
Back to the airline issue:
How about charging by the pound? Weight is what affects aircraft performance, right?
So if I weigh 180lbs and I want to bring 60lbs of gear with me, I pay the same amount as a 220lbs guy with a 20lbs bag.
Sounds fair to me!
Spacer had a good point in his post. I do sometimes feel chipped when I get charged for 10lbs too much luggage (happens in my business, where I have to carry gear and tools) while a 320lb guy (which is more than twice my weight) walks right past me (and then usually sits next to me in the plane). I can't help but to think that way, sorry.