I like to think of myself as a fair person, but I'd probably have at least a mild bias as well. I've had a lot of friends and family who have had and struggle with obesity in different ways, and had associated health problems (my father died of a heart attacked and spent his life dealing with health complications mostly stemming from obesity and smoking). Then I watch people who work at my hospital, but are grossly overweight, go to the cafeteria and get three donuts for breakfast. Also, while not universal by any means, there are frequently apparent physical differences between those who stuggle with weight, are trying to manage it, or have health problems which contribute to weigh gain, and those who simply don't care what it does to them and choose to be that way despite what it does to themselves, their family, and worst of all their children when they pass those habits on.
So yes, sometimes when I look at very obese individuals I can't help but feel little respect for them. Travelling to other countries where people are more active and obesity is less of a problem just reinforces that feeling when you come back to the US and see "Walmart specials" all around you. Similar thoughts go through my mind about smokers, especially heavy smokers - not only did both my parents have health problems from smoking, but two of my grandparents died of lung cancer. At least my parents taught me not to make the same mistakes, but it makes it really hard not to have some preconception about what others are doing to their own bodies.