Just want to throw my 2 cents in, I am not a person who is as active as he really should be. However the last time I did some time on the treadmill, I see that the amount of effort just to burn 300 calories, was pretty crazy and it makes me think twice before eating that Big Mac.
With people who are obese, I can't be judgmental because even I am not even doing the basic level of exercise per day that I should be.