Not striving on other people's misery. My motivation as stated FIRST THING is feeling good. I work in corporate America and see people all the time "on a diet". That usually means a diet coke with a whopper.
Being able to have self control, common sense and the ability to put it to good use in my opinion is the right path.
I used to be the guy who was "on a diet"... Eatin my 20 piece nugget with a liter of diet DP for lunch. I was miserable. Glad I took that first step toward kickin ass instead of sitting on mine.
It's everyone's choice.