HN is owned privately and everyone's ability to use it is at pg's discretion. pg has no duty, implied or otherwise, to provide a platform on which the principles of free speech hold. This is not true of society at large. You seem to be conflating the two.

Nearly every website is owned privately. That doesn't mean we still shouldn't seek free speech as a moral goal. What if Google censored your Gmail messages? You're using it at their discretion, right?