People should eat less. But that's a challenge by itself, because overriding our psychological needs is difficult. Plus, those needs are engineered by the processed foods industry, so it's not just one factor at play here. A good alternative would be education, but that would imply some freedom restrictions, which I won't go into details here. What Merida said is also something to consider, since people who are obese are constantly pressured to dislike their bodies in favour of thinner bodies, be it for "valid" reasons or not, which ends up further negatively affecting people.

Tldr: the whole system is broken