I accept that people outside the UK might not care, but I don't think that's necessarily the case. There's also a significant difference between making the mistake in casual conversation and on a formal document.
It's not when people mix up "englisch" with "walisisch" and "schottisch".
I'm sure you don't know and care that southern Peruvians from Arequipa like to be called Arequipaños and wouldn't like being mistaken with Northern Peruvian from the Jungle etc. Thing is they're the same to any outsider.
To the outside world, most Americans are and sound pretty similar though. Sorry if that offends you.
Canadians live in America, and get peeved when people call them Americans. Doesn't make them any less Americans, though.
You have no right to demand that.
Additionally, you have no idea about the connotations. You may find it offensive, but it is not. Not at all.
This distinction has traditionally never been very important in Germany, so people didn't habitually make the distinction.
That's exactly the point: you have no idea about usage and connotations in German, but still consider yourself an expert who should have the power to prescribe a foreign language.
As an aside: we're also lumping together (dancing) balls and (foot)balls. And lots of other things.
And how do we survive that? Context.
I was clearly replying to "Although entire languages get it wrong - in German [...]".
The poster I was replying to was claiming that other languages are wrong.
And I resent your accusations.
Maybe you can see the problem if I explain it in this way: you can become British (meaning "UK-ish"), but you cannot become English.
Not only is it technically wrong, but it also contributes to perpetuating the dominance of England over the other parts of the UK.
I try to clear midconceptions/misunderstands of other countries when I know better, I would invite you to do the same now you know more :)
Hopefully I can soothe some your resentment of my accusation too - I have been learning about Germany and the forms it existed in before the unification of the states in 1871 - the culture goes back a lot further than this, I am currently learning German and planning an extended tour by bicycle (when I have learnt enough) so I can get more deeply into this topic.
When the distinction is important we can express it, no problem. But when it isn't?