I don’t think any christian would say that glutton isn’t a sin, but you are being too simplistic in your comments about obesity. Yes overeating can be a factor. However the much more prevalent issue is that Western (and especially American) society has largely become sedentary and much of our food is low quality. Most of us can’t go anywhere with out a car. I cannot walk to the stores less than a block from my apartment because there are no sidewalks and the roads are high speed stroads. Many jobs stick people behind desks for a minimum of 8 hours per day and often more than that. I worked 10 hours yesterday and didn’t even have time to tear away to take lunch. Some of my coworkers had to go in today. Then the most accessible foods are low volume/high calorie. I grabbed a sandwich out of the vending machine at work a few weeks back because I forgot my lunch and it was 600 calories. Just a chicken sandwich with cheese. These factor combine to make it very easy to gain weight without really registering you are consuming so many calories while simultaneously not being active enough to burn those calories.

And as for your “we should treat” line. The only thing any sinner should be treated with is grace.