> it's also impossible to delete your own data, either on HN or data shared with the Y Combinator startups (except by some 'beware of the leopard' email procedure).

This violates EU's GDPR article 17 I believe, at the very least, thank you for raising the point.

The GDPR “right to erasure” has been widely misinterpreted. It is not a universal right to force companies to delete anything about you. It has a lot of carve outs for things like freedom of expression and public interest. When someone posts publicly on a publicly website that’s archived across the internet, it’s hard to argue that it checks all the boxes for deletion without any of the carveouts and exceptions.