>Sedentary, white-collar jobs are less arduous (and less lethal) than manual work. They also promote obesity and heart disease.

I'm always baffled by the dismissive wave of the "activity level causes obesity and heart disease" trope--because it's mostly wrong. The first world diet is the primary cause of obesity and heart disease, and it's well-proven. Starch and sugar, processed foods, a diet primarily consisting of carbohydrates. Diet is the driver, not activity level.