But on HN people tend to show their working, rather than using an irrelevant degree as a badge of authority.

There's a difference between saying "I think this is the case; here's why I think it; it needs a bit of iteration" and "I have a degree (in X); here's the truth about Y; some people disagree but they are wrong; I tried to publish this on Z but they are controlled by shills of the big industry and they squashed my free speech rights".