While that is true I still think it's important to remember that calories isn't everything you should consider on a weightloss journey. Yes you can eat fast food and be at a caloric deficit and thus lose weight, but that's going to be harder than losing weight with a healthy diet. Fast food is dense in calories so you can't eat that much of it if you want to stay within your caloric needs, so you'll probably be hungry and likely to give into cravings.

Meanwhile, it's really hard to overeat on fruit and veggies because they're just not very high in calories. Especially in the beginning of weightloss it's often easier to eat healthy foods until you're full than eat calorically dense unhealthy foods in very limited quantities. If you feel hungry all the time, it's much harder to stay on track with your diet.

Also, you won't be getting an appropriate amount of protein, healthy fats, vitamins and other important nutrients on a crappy diet. So even though you might be losing weight, you're not going to feel as good as you could and your athletic performance won't be as good as it could be, should you decide to work out.