A fair criticism. Consider: what keyboard do you think they're using to type all those thorns? Are they putting in the Unicode for it each time? Copy pasting it? I'd be willing to bet that they're using an Icelandic keyboard, and then they're just ignoring the fact that they are using it wrong. There is only one language on earth that still uses the thorn, and that language doesn't use it voiced. So no, I maintain that they are using it wrong, objectively, because the only living language that does still use it doesn't use it that way. It irks me in the same way that I am incensed by stupid Americans pronouncing Central American or Chinese names containing the letter "x" as if it's in the word "mix". If it's from Mayan or related languages, or in Chinese, that shit is pronounced "sh". It's just offensive, as someone who studies languages, to see these graphemes being tortured.
Can jou imagine if someone just kept insisting on tjping in Englisj, but tjej replaced everj instance of "h" witj "j", because "tjat's jow it is in Spanisj", but tjen tjej would ALSO use "j" instead of "y", because "tjat's jow it's used in Icelandic", even wjen tjose letters aren't being used to represent tjose sounds?
Wouldn't jou tjink tjat person was a bit of a prick, and probablj just doing it to grab attention, and, oj jeaj, definitivelj wrong?