a. Being fat has absolutely no advantage, unless you're stuck on a small boat in the middle of Pacific Ocean. It's absolute shit for you, and I should know, I've been fat for long enough. Furthermore, I'm reasonably sure that obesity-related healthcare costs far outweigh any pension savings, but I will not argue this point as I have no hard data.
Being fat is also not something you're born with* - quite unlike preferring to disappear behind the bike shed with people whose genitals are very much like yours, or having the sort of skin colour that makes Daily Heil readers foam at the mouth. So no, this is not a matter of diversity, it's a matter of people being a burden on society through either ignorance or sheer laziness.
b. Junk food (high in carbs) is in fact, per calorie, a lot cheaper than good food (high in protein and fibre). While we cannot completely change this, the state should at the very least swing the balance in favour of decent food.
When I started my long trek from landwhale to a mere lardarse, my food bills went up by a significant amount, despite eating less calories. Why? Because a decent cut of meat costs a lot more than a bag of crisps and a microwave pizza, calorie-wise.
*except in very very rare cases