Irregardless of your license the site need to comply with local regulations. In gdpr especially consent might be retracted at any time regardless of whether the consent was given or not at the time.

This is the full license you give for posting to HN:

“By uploading any User Content you hereby grant and will grant Y Combinator and its affiliated companies a nonexclusive, worldwide, royalty free, fully paid up, transferable, sublicensable, perpetual, irrevocable license to copy, display, upload, perform, distribute, store, modify and otherwise use your User Content for any Y Combinator-related purpose in any form, medium or technology now known or later developed.” [1]

[1] https://www.ycombinator.com/legal/

It almost reads like this forum is designed to be a training set

I just assume that I’m contributing to a variety of machine learning efforts when I post on HN.

That page links to another page for California residents, which includes:

Exercising Your Rights: California residents can exercise the right to request deletion of Personal Information by contacting us at [email protected].