There is a spectrum here. On one hand, people at a healthy weight throughout their adolescence who start a slow and gradual weight gain with their 'Freshman 15

There is a spectrum here. On one hand, people at a healthy weight throughout their adolescence who start a slow and gradual weight gain with their 'Freshman 15' that ends with being moderately chubby in middle age - yes, you're correct, that's not only the result of poor life choices, but it can probably be corrected with better ones. On the other hand, some people have negligent or ignorant parents and are (as a result) overweight or obese from a young age. This dramatically cripples their ability to make healthy food choices at an adult because it bakes in their psychological weight set point at an unhealthily high level very early on, and so normal attempts at intervention make their body think it is being starved. These folks need more than just life advice, they need medical intervention, or they stand a low chance of digging themselves out of their holes. And if they can't do that, it's a detriment not just to them but to society as a whole, which will eventually have to foot the bill for their medical costs later in life.