This is a topic of particular interest to me as a healthcare professional with specialized certification in reversing disease through diet. As a critical care nurse, i'd say easily 85% of the people i care for in the hospital are there for diet related diseases. Truncal adiposity (i.e., fat around the middle) has long been known in healthcare as a marker for metabolic syndrome (conditions that increase risk of diabetes, heart disease and stroke).
Society is kinda missing the point, it's not about appearance, it's about our health. To much fat in our arteries and on our organs causes dementia, heart disease, stroke, erectile dysfunction, type two diabetes, reflux disease... and the list goes on.
Exercise and diet are important for our health, yay you for attending to yourself.
I've highlighted the portions of your post I think are key: Keeping a healthy body weight should be more about maintaining good health and an active lifestyle, than simply "Looking good in a speedo/bikini" or whatever. There are far more potentially serious consequences to being overweight than simply being less attractive to the opposite sex- and I think more people should focus on those consequences when it comes to motivating themselves to lose weight.
And as for "Fat shaming..." Dont. It's just counter-productive. Unless you are a doctor and they are your patient.
[Blank] shaming is not on a doctor to do either, they can get their point across and keep it to the health/unhealthy side.
Some topics are sensitive in nature, but if you keep to the health points of it, then shaming should not be a factor.