Millions of people suffer from diabetes type 2 who didn't eat too much. Over-eating and weight gain are major factor, but so are genetics and other conditions.
By your logic we should stop funding HIV/AIDS research as well, spending hundreds of billions of dollars each year taking care of people who didn't use protection, at the expense of people who try to be responsible.
No, my logic would not extend to people with HIV/AIDS.
Why? Because the majority of people with Type II Diabetes (not all) could cure themselves just by eating less! Instead they put a burden on our health care system so they can maintain their habit.
A person living with HIV/AIDS doesn't have the ability to cure himself with a no-cost option. There's a huge difference there.
The original claim also included the word "cure", and according to that site there is no "cure." Diet/exercise only reduce the risk of developing it in the first place.