The reason some people insist on this is because they themselves value the provenance (place in this case) where the product was made, and they insist on discounting the opinion of those who care only about the end result.

When Parmesan is only made in Italy, those who care don't have to look at the label, but those who only care about the parmesan part have a hard time tracking under which label the non-Italian version is sold.

It's a question of whose effort is getting discounted.

It's not really a problem in practice. The UK follows EU food labeling rules, at least for now, and so this is a real (not hypothetical) situation.

The easy way is to make it clear through trade dress. Parmesan is normally sold in wedge-shaped plastic trays, in the cheese aisle. So are other grano-type cheeses like Grano Padana. So essentially everything in that packaging is 'parmesan-like'. For the crappy pre-grated stuff in tubs it'll have a label like 'Italian-style hard cheese'.

Same is true of Champagne. The other sparkling wines also come in sparkling wine bottles. And are labeled Cava, Prosecco, Three Choirs Special Reserve, or whatever.

Personally, I much prefer actual parmesan to other (even very similar) Italian cheeses, but am not a fan of most champagnes. So I'd say that the PDO-style accurate labeling was a net positive to me as a consumer, leaving aside the economic protectionism bit.

They insist on this because doing so makes it harder for people who only want the particular style of cheese and don't care where it's made to find any product other than the one that's been given an EU monopoly. For example, for a while Parmesan was a generic name for the style of cheese and Parmigiano-Reggiano was the PDO that people who deeply cared about the origins of their cheese could look for. This wasn't enough for Italian cheese producers, though, so they sued in court to get their PDO extended to Parmesan too. Now the generic version has to be sold as "Italian style hard cheese" and similarly vague, confusing names.

"other than the one that's been given an EU monopoly"

A monopoly is when one company has the exclusive right to sell a product. PDO does not confer monopolies. PDO protects the right to use certain labels.

The USA doesn't respect PDOs. That's fine, if that's what USAians want. That's their business. I want to know what is in my food, and where it comes from; that's my business. I rely on accurate labelling.

This ranting about "EU monopolies" is annoying. It seems to me that it's from people who have never eaten the real thing, can't afford to buy real Roquefort, and resent the europeans for having better food standards than the USA.

They resent the fact that Europeans are trying to control what they call food. Europe can easily add PDO Region/Name or whatever labeling, just like a manufacturing label -- but they'd prefer to try and alter the language to protect their industries... Notice how they're not creating new names, they're trying to reign in generic names.