Actually obesity is somewhat genetic. There are genes that code for rate of glucose breakdown, glycogen synthesis, lipid synthesis, lipolysis and all those other metabolic pathways as well as their regulators. Therefore, two people eating the same food and exercising may not loose the same amount of weight. There's also leptin and T hormones which control one's appetite, if anything goes wrong with them then the person will gain weight. So there are genes that pre-dispose for susptibility of weight gain.

Being overweight is also a symptom of several illnesses such as hyperthyroidism, cushing's syndrome, etc.

So although many times people are overweight because they're not eating right or not exercising enough, that is NOT always the case. Our bodies don't always work in the perfect ways we'd like them to, and it wouldn't be fair if we automatically judged someone by their appearance when infact we don't really know what's happening inside.

p.s. I'm in no way promoting obesity, but just wanted to make clear that sometimes it does have a genetic/medical reason.

I'm not always right, but I'm never wrong -Garfield