They just eat too much. Of course there is the quality of the food, the hormones etc, but bottomline is they just eat too fucking much and they don't move enough to burn it. A lot also are presented huge portions and wolf them down without even stopping for a minute to see whether they are still hungry. Or keep a bowl of sweets to munch on and pop drinks while burning the bare minimum.
I spent more than 5 years as a student with sole cooking utensils being baking paper and a frying pan, bought food at Aldi (which is dirt cheap so probably not the greatest stuff), basically survived on pizza (deep-frozen), canned fish, baked chips and sandwiches and some fruits/veggies (but wasn't poor enough not to be able to afford enough food and stay hungry). And a lot of other people in dorms did pretty much the same, so it's not like my genes are special that way. Most of the people I lived around were normal weight and stayed like that.
Europe is getting fatter too though (UK is already pretty bad, if not extremely bad). Even the French are getting fatter.
I'm pretty neutral on actually punishing those eating habits. I've been pretty open about disliking them aesthetically though, e.g. when it comes to dating, then it's a no-no (yeah, I'm pretty shallow, one could have a great personality, but jeez, fat is cold and icky, so it's never moving into the physical).
