I agree that there are contexts where emoji may be inappropriate (definitely Github, I'd disagree about HN, because I think this place needs to lighten up) but they do clearly have utility for a lot of people.
It does seem harsh at times, but when you start letting short/irreverent/low value content through and you end up with reddit.
Many brilliant minds throughout history were also possessed of a keen sense of humor and a playful attitude which many HN users would consider infantile and puerile in modern culture. The implied inverse relationship between humor and "quality" of either intellectual or technical merit doesn't really exist, it's a cultural affectation, a taboo born out of the fear that humor breeds normality and normality brings the Eternal September effect.
However, HN doesn't often attach the same stigma to hostility or banality as it does humor. As a result, hostility and banality tend to flourish and become a means of virtue signalling because they aren't considered to be inherently toxic, merely bad form. Maybe dang wouldn't have to spend so much time talking users down from ledges if the culture here didn't require people to take everything so damn seriously.
And people have been complaining that HN is turning into Reddit since the beginning. There's plenty of content on Reddit of equal or greater quality than on HN, and plenty of HN users who also post on Reddit and elsewhere, and plenty of low value, low effort content here. Having that content also be humorless doesn't really add value.