I get that it's hard. I've been through it myself, went from a BMI of 32, which is obese, to 23
No. Stop it. Congratulations on your weight loss, but don't for a second think you have any idea what it feels like to live inside the body or mind of someone who is morbidly obese. For someone who is 6' tall, a BMI of 32 weighs 235 pounds. If you're a man, that probably means your waist is 38-40", and you can pretty easily wear a 2XL t-shirt (XL if it's a company that makes them big). Someone that size can switch to a 1700 calorie diet and succeed, because that's probably not too far out of touch with the equilibrium their body has established.
My BMI is 56. At 6', I weigh 410 pounds. My equilibrium consumption is 3300-3500 kcal a day. If I switched to a 1700 kcal diet tomorrow (I could - I'm a pretty smart guy, and I know what to buy to get the job done), things get unpleasant very quickly (I've done this before, so it's speaking from experience). Most of my metabolic processes would turn down - even though I've plenty of fuel reserves, my body would start signaling starvation. Not permanently, but it takes time for the body to make the shift from burning mostly carbohydrates to burning mostly fat. This feels like the worst hangover in the world - no OTC medications cure it, nothing even helps. Sleep is hard because everything hurts; concentrating is hard because my brain chemistry is all fucked up; conversing is hard because my moods are flighty and prone to change. The worst part of all of it is that making all of that go away is a plate of peanut butter sandwiches away. Most morbidly obese people who go for a 1700 calorie diet fail at that point, before they even get started.
Even if I make it through that, 1700 kcal isn't enough for me to function at 410lb. I'll lose weight very fast, 5-10lb a week, which is dangerous weight loss, and I'll be constantly exhausted. But, I'll still have difficulty sleeping, because I'm losing weight so fast my brain can't get a handle on any kind of rhythm or equilibrium. If I'm also exercising, I'm making the problem worse, and I might be doing permanent damage to myself, because I can't tell whether that pain I'm feeling is because I injured myself on the treadmill or because today is just the day that that joints in my leg are going to be especially painful (because that's a thing that happens when you lose weight that fast).
Assuming I can stick with it (which is a big assumption), at some point well shy of my goal weight, probably after 80 pounds or so of weight loss (which could take as little as four months), I'll very suddenly stop losing weight, because my body will finally come back into some semblance of equilibrium. I'll still be constantly exhausted, because I'm barely breaking even with my caloric intake, but I'll be accused of cheating by my dietician (which is untrue) or I'll be told I just have to exercise more, which is hard because I'm still in constant and new kinds of pain every day. Joints, tendons, and ligaments used to carrying the much larger me still haven't completely readjusted to carrying a smaller version, and if I stress them, they move in uncomfortable ways. So now I'm stuck at a plateau, in a self-hating limbo between being a self-hating fatass and a self-hating skinny person, and I might be stuck there for MONTHS before I can make progress again. Or, I can eat the food I enjoy, because I know that's comfortable. And suddenly, I'm back where I was again.
The only thing you said that wasn't nonsense was the statement about deficit, but it doesn't mean the same thing for morbidly obese people. I've recently started taking Cymbalta for my anxiety, and it has decreased my appetite (or curbed my anxiety enough that I don't stress eat as much). I've changed literally nothing else about my life - I still eat shit, and I still eat too much, and I don't exercise - but that small switch was enough for me to drop about a pound a week over the past two months. THAT's healthy and sustainable weight loss, but it demands that people take honest assessments of what they do and set reasonable goals that fit their needs with health professionals who understand the special constraints that accompany the very fat. And most health professionals, FSM-love 'em, REALLY don't.