Taffy: It's now documented in detail that people find the arguments, facts and research that corroborate what they feel about the world. You are just demonstrating that these days. If you feel that being slim is the top health priority in your case, then you will find articles that support that.
I agree with you, though: I believe that fat people bring all sorts of illnesses to themselves, starting with diabetes. On the other side, are most slim people healthy? (I would say so - I am sure you have found many articles to this effect already).
Regarding "bad" food (like meat, restaurant fast food, fried food, and mostly added sugar food), whatever it is, it is my belief that a small portion once in a while can't hurt. Daily consuming "bad" food though is certain to hurt. Programming the mind of a child to avoid restaurant fast food, fried food and all added-sugar foods (90% of grocery stores in North America - how is it in the UK?) is virtuous in my opinion: You have the power to prevent tons and tons (over decades) of sugary food for example from entering a person's system over a lifetime.
I salute your efforts to learn about food. I believe we are what we eat.