If only it was that simple. 
Overweight people very frequently do 'take responsibility' for what they eat. What do they do when they decide to do something about losing weight? Usually they decide to go on a diet or some other programme of 'healthy eating'.
Perhaps they go around the supermarket and switch to foods labelled as 'healthy', 'low fat' etc. Unfortunately these labels can be very misleading, the foods may be low in fat but high in sugar, or maybe just ever so slightly healthier than the regular version, but still not really an appropriate choice - maybe a 'healthy choice' ready meal.
Maybe they decide to try the latest popular diet. Maybe they lose a bit of weight. But then they put it on again plus a few pounds and blame themselves for not having enough 'will power', so do it again and again and end up heavier than before and with added low self esteem from the repeated failures. These diets have HUGE failure rates, which is always put down to character flaws in those who follow them, rather than accepting that they are just unsustainable for most people.
Ah, but maybe somebody tells them that yes, those diets don't work, why don't you go to one of the slimming clubs, they are more about changing your eating habits for life. Maybe they go an lose some weight, but again after 5 years the weight is back on again because for most people they don't work in the longer term.
So maybe our overweight person, who is now obese, goes to their GP for advice and are given the standard government Change 4 Life advice (backed by their partners the confectionary manufacturer, Nestle) about healthy eating - switch to low fat (hidden sugar) foods.
I sincerely believe that many overweight people have "taken responsibilty" for their weight more than most people. I have watched my mother struggle with her weight for my whole life, she's been on so many diets, tried so much to control her body and appetite. I don't have an impression of her as a greedy or lazy person. If anything she put on most of the weight whilst being a busy mum with five children to look after and a full time stressful job and suffering from depression. I don't remember ever seeing her stuff her face though I accept she may have done when I wasn't around. And yes, after years of failed dieting she has had bariatric surgery on the NHS. She was so embarassed about it that she didn't tell me or my siblings what she was going into hospital for. Its not cheating to lose weight that way, and its not an easy route. It hasn't been 100% successful in my mum's case, but it is successful for many people. She's trying to go back to her post-op good diet now.
Campaigning for easy to use labels on food, for manufacturers to be more responsible, to reduce food advertising particuarly to children, for the government to make sure its advice is evidence based... these things won't take away the responsibility on the person putting food into their mouth. Of course it can't be done without them, but as a society we can try and make it easier for them to make better choices, rather than set up an environment for them to fail in even when they are trying their best. We ALL like to think that we aren't influenced by advertising, but if it didn't work they wouldn't spend so much money on it. These companies make money out of selling us too much food and diets that don't work.
I like the video linked to earlier which suggested that eating plenty of fruit and veg, taking regular exercise, not smoking and drinking only in moderation delivering health outcomes for everyone regardless of their weight. It gives a bit of hope, since losing weight permanently seems to be a long shot.
I have excess weight myself which is reducing a bit now that I am trying to eat better and exercise more. I don't know if I'll ever have a healthy BMI, though I'd like to. It's blooming difficult trying to find a way of doing it which won't result in bouncing back to my original weight (or higher!). I do have thyroid issues, and have had some mental health issues that meant I was a bit crap at self care. I'm trying to being mindful about what I'm eating, and to eat smaller quantities of more nutritious food.
I do think that people who have excess fat should be treated with respect, and given as much evidence based information - and if necessary - treatment as possible. I don't like the idea of surgery personally, and I hope I'm young and healthy enough to do it without that, but for people whose mobility is restricted so much that they cannot exercise it may be a reasonable option. I've also heard of success with treating Type 2 diabetes by putting people on the post operation diet, without the surgery.
I guess that describing people as greedy and lazy is just a less kind, observing from the outside way of saying Eat Less, Move More. But it is a really savage attack on the personalities of people who are struggling with contradictory diet advice, a world full of very high calorie food which requires very little preparation and can therefore be eaten on auto pilot (rather than mindfully). 'Will power' is hard to sustain in the long term, and when it disappears the person is left with habitual and emotional eating, susceptible to advertising and basic impulses to eat something now.
Telling people they are greedy or lazy doesn't give them the confidence and self esteem to look after their bodies. It just pushes them into that emotional eating cycle of eating something for short term comfort, adding to the problem. It doesn't give them information about how to eat less or how to move more, it just tells them that their character is fundementally flawed rather than them being a human being capable of a different pattern of behaviour.
If fat shaming worked we'd all be slim, nobody (well almost nobody, sumo wrestlers excepted) wants to have lots of fat.
If you saw me on the street as a size 22 you might well think I was a greedy, lazy fat person, if that is what you are inclinded to think about people who have my body shape. If you told me so I'd laugh in your face. Not because I don't know I have fat, but because I have lost 6 stone already, you have no idea whether someone is being greedy and lazy and putting on weight, or being moderate and active and losing weight just by looking at them or weighing them on one occasion.