Science: "obese people cost more". More health care cost, more fuel used to fly them around, even if they fit in 1 seat.
Not a fan of the pro-fat movement. Most discrimination is traditionally towards things people can't change. The whole gender thing has moved that goalpost a bit, but a man wearing a skirt while flying does not cost the airline extra. If my grandparents and my parents all died of cancer not due to lifestyle choices I should still get health insurance. If I smoke, my life insurance premium goes up. That is fair IMO. Being fat is a choice.