Reddit, Instagram and Twitter all require emails, and they're some of the most spamful services I have seen. HN requires nothing but a unique name and associated password, and if there's a lot of bots here then I guess they're running really sophisticated NLP.
Now of course, HN is more domain specific and niche than other socials so I know it's a bit unfair to compare spam because of course spammers would be more interested in the more populous and general purpose social media, and it's possible that spam and bots on those other services would be even higher if not for email registration, but there's simply no data to support that : email registration is cargo-culted by any remotely user-oriented service without thinking if it fits.
And there is a very good reason to think that email registration is just a dumb lazy hack to delegate problems instead of solving them : come to think of it, email fights spam! How do they do it, by delegating to another email service? Email registration all the way down? Of course not, they just run a bunch of really simple stats on the text to reject the obvious 99% trash. Are reddit and twitter too poor to pay for markov chains running on every text submitted?
