Fully agreed. If it was genetic, then it would be impossible that the obesity epidemic suddenly exploded almost overnight over just the last couple of decades. How would one explain that most (continental) Europeans remain slim if most obese Americans are of European stock? New genes don't appear independently in millions of babies simultaneously. And people weren't starving a few decades ago.This excuse of obesity being in the genes, or is a result of "depression", is a lot of crap.
I say that it is selfinflicted and that you are what you eat!
If you eat moderately, eat healthy food (READ those nutrition breakdowns on the food you buy), and you exercise regularly, it's guaranteed that you will remain slim and decent-looking unless you have a RARE SERIOUS DISORDER (not "genetic predisposition"), but this is probably less than 1% of the population. Of course it's a bit harder for some than others due to genetic predispositions (e.g. gender being one genetic factor that is known to have an influence), and for them it will always be slightly harder, but this represents only a TINY percentage of the causative factors; these metabolic rate spreads etc. were no different 50 years ago when this problem was virtually non-existent.
It's just physics. To do work your body must burn energy. If you burn more than you take in via food, you will lose weight - 100% guaranteed, it's physics. You DO NOT absorb fat from the air you breathe.
I think the primary cause is that people no longer believe they are responsible for their own actions. Parents blame "genes" or "society" or ANYTHING they can think of JUST NOT THEMSELVES ("oh, it's just genetics, I can't help it!"); children in turn blame parents, somewhat rightfully, for being horrific role models that pass on the same idea.
I think one problem is that people don't realise just how much junk is in a little bit of junk food. You think "one little packet of chips" or "one chocolate" or "one glass of coke" or one KFC takeout - most of our foods, especially sweets and takeways, are almost pure fats or sugars, there's a HUGE amount of cr-p in a tiny serving. Cut out 90% of that rubbish for one month and eat mostly healthy meals (ideally home-cooked) and five servings of fruit/veggies daily ... in the beginning it might be tough, but your body actually quickly 'gets used to it' and then prefers the healthier stuff. When you eat junk regularly, you can't taste the fat or sugar anymore, you get blunted to the taste. But when you re-adapt to a diet more fit for a human, you start to be able to taste that gunk and don't enjoy it as much.
Healthiness is also ideally a 'lifestyle' - you can't easily just change one component; e.g. if you start an exercise program but still mostly eat junk, it will likely be ineffective - you won't get as much benefit from the exercise, and you will feel cr-ppy and demotivated when you exercise, because you aren't eating the kinds of foods that your body needs to have the energy to exercise. Change several things at once and it all just works better.