That said, this particular issue should not have been turned into a state-politics issue. The element in question seems to be a language selection rather than a country selection, so the very first argument ("TaiWan flag should not be placed along with other REAL country flags") is a bad one regardless of how you think of Taiwan's political status.
I also agree with another commenter that said the maintainer dealt with this really well. Kudos to them!
But filing tickets demanding to remove something from a CSS library because it "isn't a real country" definitely is a political statement. Which, for me, is always very unwelcome, but quite mundane at this point.
If a Quebec separatist wrote some software, they might give Quebec a flag of its own like a country in the software. (I've seen it before!) Political statement. Or they could leave it out and use the Canadian flag -- also a political statement in the eyes of some. There's no way out of it, really.
It would be sad and petty if a GitHub PR spam war started over the flag in question. But politics is often sad and petty.
Not people focused on the purpose of the repo.
Languages are already quite political, but maps and all their borders and city names are much worse. Some borders are disputed and both sides have made the distribution of maps with the "wrong" borders illegal, the Catalans hate to see the Spanish names of their towns used in the Spanish version of the website, sometimes borders are moving fast and the inhabitants of newly founded countries usually feel really strong about the correct representation on every single map in the world, and even if you use maps without borders or labels at all, it could be illegal to plot some kind of harmless data on it, like wind speeds that have not been published by the country's authorities.
Stuff like this inevitably floods the inboxes of a lot of companies, so I'm not surprised at all to see it happen on GitHub.