:It's a medical problem that they caused themselves.
Being fat is a choice.
What about those with thyroid disorder? Being fat there isn't a choice, it's a complication.
You argue that since they will eventually be a burden on a public health care system, they should be taxed to help counteract their affect on the system. Does this mean that those who suffer from disability should have a "disability tax" because complications from their disability burden the health care system?
How would this tax differentiate from those who are fat from sloth, fat from medical condition or environmental factor? Where does it stop? Should children be taxed because they're more prone to certain disease and would create a burden on the health care system?
tl;dr: He opens a can of worms of taxation without representation.