"It's the balance of the overall diet that's important, not every single of item of food consumed.
Do the food police posters exist solely on 'good' food? No 'unhealthy' food ever?"
All the stuff about balance and moderation is true, as is the conflicting data about whether saturated fats are good/bad/necessary/evil... but it totally misses the point that, if someone is asking whether a processed cheese pasty is junk food, then they're not making informed decisions about the balance of their diet. If you can't identify which food is low in nutrition and high in sugar/salt/fat, then there's no hope of striking a balance.
If I consider a processed pasty to be quite decent and healthy (three veg and calcium), then maybe I'll have one for lunch and treat myself to a McDonalds for dinner -- I know fast food is 'junk' but that's okay, because I've already eaten a decent lunch, and so a balance has been struck.
It's taboo to say this on MN, because it sounds patronising or snobby, but some people genuinely have no idea about the nutritional content of food. (I am allowed to say it, though: one of my parents has the worst diet known to Western man.) I think it's more condescending to act like this isn't a problem; as if everyone's obviously eating their cheese pasties as part of a well-balanced diet: cheese pasty for lunch, but quinoa salad and grilled tuna for dinner, of course.
If you've been brought up with no clue about nutrition, it really muddies the waters when no one's ever allowed to make a public statement about any food choice without endless, convoluted, well-meaning discussion about how no food is good or bad and everything's completely fine as part of a balanced diet. This is right -- but all the pedantry, nit-picking and snide references to 'food police' actually denies some people the basic information they need to form that balanced diet in the first place.