i agree, weight is always a case of calories in versus calories burned, simple maths.
Also, however, nutrition is very important, as is understanding how foods are metabolised, as it is not just the quantity of food eaten, nor indeed the calories, but how the foods feed the body, or poison it, how they are metabolised, or how they affect the overall metabolic ticking over of the body.
Also, lack of exercise is not simply a question of laziness. Most jobs 50 years ago were much more physical. Most jobs now are sedentary. This in itself changes the number of calories burned, muscle tone, muscle strength, posture etc. Also, simple things like the introduction of central heating has had an impact on the number of calories the average person burns. This is not about laziness, it is about gradual lifestyle changes in our entire culture over the past 60 years.
Finally, i agree exercise, even twenty minutes of walking the dog every day, is essential, or indeed half an hour of moderate housework, or of moderate gardening...there are plenty ways to build regular and moderate exercise into life..taking stairs instead of escalators.. parking the car a bit further away and walking that bit further there and back. However, lack of exercise is not simply a matter of laziness. The past six months my ability to exercise has been radically reduced by a pelvis/back injury, and i was barely able to walk for eight weeks, and have been very restricted in what i can do in the following four months. I used to run around 20k a week. Now the most I'm allowed is a 20 minute gentle walk, and though my back is recovering, my pelvis is more stubborn, any more than 20 minutes, and any faster than a gentle stroll, and my sacro-iliac starts clunking around. Recently i was given the all clear to go walking in the sea, which i did, and now this week my sacro-iliac is clunking again... all i was doing was walking my dog, being careful, walking slowly and it just started clunky clunk, with the usual pains, stiffness, and i'm back to painkillers and anti-inflammatories, and small and slow steps and a lot of pain. It drives me nuts. I can't swim (rocks the pelvis)... I can gently scull on floating on my back with floats supporting my back and my neck, I can't cycle (same reason), I can't even do pilates (I researched hundreds of exercises online, started doing them, took photos of me doing them so i could ask my physio about if i was doing them properly and she nearly had a fit, put a pen through 99.9% of them, and gave me four or five very basic stretches as safe to do)... all i can do is keep up the gentle walks and hope over time this gets better... that's not laziness, that's just bad luck.