Gets upset about obscure punctuation mark used incorrectly in a non native language...
Do you mean the language is not the native one of the person who used it?
Because the Irish language is one of the UK’s native languages and the fada is no more obscure in that language than an acute accent is in French, for example.
Anyway, the issue is not primarily the fact that the fada was left out. Nobody expects people to be fluent enough to use the Irish form of the name. That’s the point actually.
Lots of Irish names used in the UK (and in Ireland tbh) should have a fada but don’t, even though, strictly speaking, the meaning and pronunciation of the word is changed, and often not for the better. Orla is an example, or Sean. I doubt people get hassled about it in general? People just pronounce the names as if the fadas were there and ignore the alternative meaning (if indeed they know it, which they most likely don’t).
In this particular case however, it’s the history of the tactical use of ‘Eire’ by the UK establishment that’s the issue. I know people often aren’t aware of that history unfortunately. But that’s why it shouldn’t be used in English if you don’t want to cause upset. The reasons it should be avoided are historical ones and, though most users are certainly unaware of this, its deliberate use can still indicate a certain mindset today.
Personally, I prefer to give people the benefit of the doubt and trust that pp probably wasn’t aware of the issues.