From Wiki:
"In even the earliest references he is fierce yet good"
Much like?
'The warlike fierceness of the unicorn is referred to when Ephraim and Manasseh are described as being like the horns of unicorns. [Deu 33:17]; The terrifying destruction of Idumea is completed when God sends unicorns and wild bulls to attack the people. [Isa 34:8 see also Psa. 92:10 & Psa 22:21]'
'If, however, the girl was merely pretending to be a virgin, the unicorn would tear her apart.'
Again, from Wiki: "Chinese dragons (simplified Chinese: 龙; traditional Chinese: 龍; pinyin: lóng), and Oriental dragons generally, can take on human form and are usually seen as benevolent, whereas European dragons are usually malevolent though there are exceptions (one exception being Y Ddraig Goch, the Red Dragon of Wales)."
I tend to think of D&D as a western game, not an eastern one. There are exceptions, of course, but that was an oversight on my part. At least gold dragons were actually modeled after eastern dragons, unlike the rest.
But even there, the Seelie court (including hobgoblins) was considered benevolent and the Unseelie court was considered malevolent.
The Seelie Court is known as the good court because its pranks are _not_ of the murderous variety. They're not good. Just not evil.
The fact is that early versions of DND drew on real world mythological creatures to some extent which had both good and evil and that is being thrown out now. Gary would roll over in his grave. Culture be damned.
I have to admit, Gary rolling in his grave is almost the Hitler of D&D debates. He separated from the process and disagreed with most changes that happened after he left, decades before now, but somehow he'll care more about things like this? It's a disservice to his memory and a gross assumption to invoke him when something bothers you.
Personally, I'm not really sure I agree with making, say, gold dragons not good... but I also didn't agree with leaving alignment in the system at all, so I can ignore that line on dragons like I do on everything else. If it's Eberron, the gold dragon can be evil and the red dragon can be good, and if it's Dragonlance they can be the reverse, and hopefully at the end of the day it matters more about the intentions, motivations, and actions rather than a word in a monster manual.