No - you're wrong (and how the heck did you get modded as "insightful"?).. I don't get uncomfortable because there are more fat people in the US. I do hate to sit next to some cow - even if he/she is what would be called "normal" in the midwest these days - on an airline. I'm not asking for first class armroom; I'm just asking that the person next to me doesn't spill over into my seat. I'm an older, big guy myself, but I'm fit, and I'd appreciate it if more people in the US made the effort, too.
And whaa, whaaa, whaaa, about being "bombarded" with unrealistic body images - if they had any real effect on the psyche of overweight people, then perhaps we overweight wouldn't be the new normal.
I live in South America and return frequently to the US. The first thing that I notice when I land in the US is how overweight people are. It's not that there aren't fat people in Brasil, Argentina and Chile; it's just that it's not the norm.