A lot of the things humans put in their mouths just aren't safe long term. We're pretty good at making suboptimal long-term choices.
Without being able to run experiments on real human bodies over full life spans like I suggest here [1], it's impossible to quantify.
[1] https://news.ycombinator.com/item?id=25235013 (I advocate for this rather frequently)
Small amounts of any of those "bad" things is just fine. The problem is that many people have come to see them as the core of their diet, with vegetables as an unpleasant supplement to be minimized. Learn to cook vegetables well, and vast frontiers of interesting, delicious food open up.
Indian food is an excellent starting point[1], for either vegetarian or vegan eating. For that matter most authentic Asian cuisines are heavy on the vegetables, with small amounts of meat for flavor, which is also a very healthy way to eat (especially if you substitute whole grains for the white rice).
Plenty of other cultures have thrived on vegetable-based diets. It's really not that difficult. You just need to get over the notion that "food" consists of a meat main dish, a starch, and a desultory, obligatory vegetable side.
[1] https://www.priyakrishna.me/indianish is a current favorite of mine.
Think of a dish composed mainly of "vegetables, whole grains, and beans" with minimal carbs and even more minimal butter/oil. What is the recipe? Then, consider if it tastes good - as good or better than similar recipes where more carbs and oil is used. I've been cooking a variety of meat and vegetarian dishes of various cuisines for years and I know of no such dish I'd want to eat with regularity. Brown rice, steamed chicken breast, and cauliflower just doesn't cut it for my palette, and I suspect the same for the majority of people who know how good a Sunday roast or pizza tastes.
Controlling total calories is important in weight loss, and that's a matter of portion control. A diet with a good proportion of fat will be fairly satisfying; you just need to limit the total amount of it. That'll still leave you a little hungry. There's no magic that makes calorie deficit pleasant. Tweaking the ratios can make it less unpleasant, a matter of personal taste.
It doesn't need to be junk. You don't even necesarily need a calorie deficit, if you're happy with your weight. There exist good vegetarian and vegan diets with appropriate amounts of fat and appropriate total calories, and they don't at all resemble "brown rice, steamed chicken breast, and cauliflower".
If carbs are bad, you can't have those.
The problem is that some foods have nothing but carbs, and if you eat a lot of those, you'll either consume too many calories overall or fail to get necessary nutrients. So eat fewer white, starchy foods like potatoes, and more leafy foods, squashes, and other colorful foods.
Similarly, whole grains bring a lot of vitamins and fiber, while refined grains like white rice are reduced to just the starch. It's just fine that those whole grains also have carbs in them. That's actually a good thing, becuase you do need calories for energy. You just need more than that.
Most people can get away with eating whatever they want with a modest amount of rigorous exercise each day. Granted, they still need to control their food intake and ensure they are getting required nutrients, but that's pretty straightforward.
You can get calories from protein, fats and carbs, so choose a balance diet.
“Life ain’t worth a dime without a little colesterol” Leah Chase
I mean don't get me wrong, at home we have a fryer and we make the odd load of homemade chips as well and they are the tits, but it's not the same.
We used to be able to get solid blocks of frying fat, probably was beef tallow or something like that, but it's all saturated fats (I believe) and bad for one's health and the like. According to the wisdom of the time anyway; I don't know, there may have been some lobby behind it (like how the wheat lobby made fat the boogeyman, and now someone is making the sugar / carb industry look bad).