The most disturbing part of all is that fat free is not healthy
America has an image problem--anorexia and bulimia are rampant, but obesity is just as much a rampant societal disease. The problem is, if you happen to be one of the people afflicted with genetic obesity, diet food isn't going to help you. If you are obese because of lifestyle, diet foods might help, but just eating 98% fat-free cookies and meat won't make you drop those extra 100 lbs.
Diet junk food tends to be just as devoid of nutritional value as its fattening counterparts. This means that you aren't getting the fat, but you are also not getting any protein, vitamins or other important nutrients.
On top of that, fat is an essential nutrient. Excess is bad, of course, but an excess of anything can be a poison, and fat is no exception.
Health food, not diet food is the way to move back towards a healthy lifestyle, and a balance between the double-edged sword of obesity and anorexia.
Besides, gluttony is still a sin, no matter what the fat-free status of your potato chips is.