I don't know if it's a case of fat = evil, but I can vouch for the fact that fat people are treated differently than their thinner counterparts.
When I was 130+ pounds heavier, people wouldn't look at me. Men wouldn't hold the door open for me, sales clerks took their own sweet time about helping me in stores. People were amazed that I was smart enough to be in graduate school, because the common perception of a fat black woman is that (1) she's not very intelligent (2) she's lazy, and (3) she must be on welfare.
Now that I'm smaller, my life is completely different. People actually make eye contact. And not that my self worth depends on what men think of me, but men not only hold the doors open for me, but they actually SPEAK now, when they wouldn't before.
(Does it show that I'm still pretty bitter about how fat folks are treated?)
I agree with the sentiment that as a nation, we eat far too much and move far too little. It's really difficult to point to one particular cause, but I think that our propensity to look for the best "value" has a lot to do with it. For example, these days when I go to a movie, I always order a small unbuttered popcorn, but the person behind the counter ALWAYS says "Would you like to upgrade to the large for 50 cents more?" -- never mind that there's four times the amount of popcorn in a large bag as there is in a small -- but we go for the gargantuan sizes because it's a "bargain".
I also think that the way that American cities are designed has a lot to do with our sedentary lifestyle. We moved out to the suburbs, our jobs are still mostly in town, so we spend half an hour or more each day plunked down on our butts in our cars. We hate the idea of public transportation, and most municipalities refuse to support initiatives. We're more insular, we like to do things as quickly as we can with the least amount of effort. Our "creature comforts" have contributed to our greatly expanded waistlines.
Okay, I'm gonna stop here because I feel a blog entry coming on. ;-)