It is a common suggestion but I think it would be a mistake to require people to post reasons for their downvotes. It would produce a ton of noise (because people would just make shit up) and dramatically increase meta-bickering about downvotes, which we already have too much of.

Edit: here's a partial list of past explanations about this, in case anyone is interested in seeing how it has come up over the years: https://news.ycombinator.com/downvote-reasons

There is little need for formal studies. HN is very surely different from «other social media platform[s]»: you must have never been on Reddit or YT, to provide examples of diametrically opposite places. A quick look at information density and "where the uttering came from" (say, above the neck, below the hips or other guts) should clearly show a massive, radical difference. That feelings influence voting, in terms of "hear, hear" or "thank you", is not undesirable: it is still agreement on reasoning. Expression of disagreement through downvoting is limited already through a technical limitation, which also contributes to indicate the form. Some foolish snipers (hitting without leaving any justification) are around: bad apples are not curbed, also because it apparently is not a mission for HN to create an optimal system of moderation and debate.

In fact, there are several shortcomings to adopt HN as a model for moderation and debate - it was evidently not the objective. But civilization wise, there is no comparison with many other places.

By the way:

> a story HN members tell themselves to feel special

Please. Accusing others to have unclean grounds in their evaluations, gratuitously? And, when one is "special", it is not out of some free membership that confirmation comes.