Look I'm the last to demonise food, I hate the posts on social media about aspartame, Coke stripping off rust (yes, citric acid will do that, rub a lemon on it) and McDonalds scaremongering. But a cheese and onion pasty sort of is junk or if you don't want to call it that, all filler no killer.
Its not so much what it has in it than what it doesn't - potato, leek, onion, in the quantities that it has, barely register. (Did you know potato doesn't count as one of your 5 a day? Even a jacket potato baked in your oven at home?)
So take that cheese and onion pastry and put a slice of it with a side salad and its not so bad. Take a whole big one and it kind of gives you such an energy density whack with so little fibre or nutrition that no it won't kill you, and yes it will fill you, IF you need filling - (if you don't burn it you store it) - as a one off or occasional, fine. But in terms of long term nutrition, it gives little other than a big energy whack that you then have to burn off, and leaves you lacking some fibre and micronutrients that you will then want to get from elsewhere for optimum health.
They are the kind of things that manual workers can totally get away with eating regularly with no ill real effects if their cholesterol is not prone to being high and they are not genetically at risk of cardiovascular disease. Cheap, satisfying, tasty.
The rest of us, as on occasional "treat", fine, if you are out and about and its the only think you want or can afford, if you aren't fat, don't have high cholesterol, constipation, gastric reflux, etc etc...sure.
Not worth clutching your pearls about if you get one once a month when out in town and you don't want to sit down somewhere and faff about and leave a tip or whatever...
You get my drift.