People that can prove that they really have a medical problem to lose weight are excluded, but people that can lose weight and are too stubborn to do it should be fined. This should help them understand the dangers that obese people are putting their own life in danger. They are having a higher risk of getting diseases and even death. This should persuade them that their lives are at risk. Would they really be that Stubborn???
Would be over healthcare costs. There's only one problem. Studies have shown that overweight people cost less overall in healthcare than thin healthy people. The main reason...They die sooner. A lot of them don't make it to be a very old age, so obviously they aren't going to have old people problems which cost a lot of money.
So if you want to fine people over healthcare, then I guess that burden should be on the elderly.
Fining fat people who refuse to lose weight would result into all sorts of difficulties. How do you determine that the person has actually tried to lose weight? What if they've trued and failed? What if they can't lose weight for a medical reason? Would they have to go through a medical evaluation? Who's going to pay for it?
A person's health has no impact on others. While it is certainly not a good choice for people to be overweight, those people pay the consequences through ill health, more doctor's visits and the like. Some people are medically unable to lose weight or are desperately trying. It is a matter of personal choice and we cannot infringe on their freedom.