Obesity is a problem, but if you want to help them, being nasty is not the right way to go about doing it. No one is perfectly healthy - not even doctors and certainly not medical students, going by what I've seen. Everyone makes poor eating habits or makes some choice that is less than perfect.
I have had many lectures on the consequences of obesity, the mechanisms of obesity and the current treatments that are available. Losing weight, once you are obese, is EXTREMELY difficult. Your brain literally fights against you - Neuropeptide Y, Leptin, Ghrelin, all of these molecules will fight against any attempt to lose a lot of weight. It's not easy, and takes an extraordinary amount of willpower to lose weight through dietary changes alone (which is why most fail). I don't judge anyone by their personal struggles with their body images - leave that to themselves. Yes, obesity does put costs on the Health Care System - so does Alcohol use and abuse. Given that I am a (non-religious) teetotaler, does that give me the right to judge and hurl abuse at those who do drink, or perhaps abuse alcohol? No.
No one is perfect. I will remind patients of the scientific fact that Obesity is bad for you (and I am a medical student and I was/am a scientist - I know my science and I've read my papers. Sorry Fat Acceptance movement, Obesity IS bad for your health. Very bad. Some of those fat-acceptance folks are approaching "my smoking is perfectly healthy!" levels of delusion when it comes to the health problems associated with obesity - by claiming that obesity causes no problems whatsoever. Which is wrong on so many levels), but I'm not going to scream abuse at them since they are still human beings who deserve respect, fairness, and should not be solely judged by their weight. There's more to a human being than how much they weigh, and its tragic that so many people fail to understand that.