As for the people that think it is okay to make fun of fat people and that it might even encourage them to lose weight, it will likely have the opposite affect and make them more depressed and eat more.
With that said obesity is also likely the result of emotional problems that need to be addressed. I don't think it is as simple as someone being addicted to food though it probably leads to that.
And yes, there are also other causes to obesity like processed foods, tv, video games, etc.