Censorship by definition is "the suppression or prohibition of any parts of books, films, news, etc. that are considered obscene, politically unacceptable, or a threat to security", with the clear understanding that attempting to bypass it by publishing elsewhere will be likewise censored and likely punished. Routine maintaining of order & interest on a private site is NOT censorship; you are welcome to publish your…
But this is the thing, other sites have similar idea of "censorship", you cannot post your own things. So, if people are centred on specific sites, where can you post? Maybe they will not kill you physically but surely they will kill your electronic life. Also question is following if people gather on private site are those sites private or public?
There are plenty of sites where you can post pretty much whatever you want. HN likely frowns on self-promotion, as it would fast turn an informative news site into a bunch of "look at me!" content few are interested in.
Publicly-accessible privately-owned sites are still private, just like stores "open to the public" - you're welcome to come in and participate as the business sees fit, but promoting yourself (unless that's the point of the site) is usually frowned on and not leaving when requested is punishable trespassing.
No, they're not "killing your electronic life". Go to networksolutions.com (or wherever), register your own domain, and publish whatever you want (a few generally-accepted legal limitations aside, like libel or obscenity or state secrets). Promote it thru advertising, Twitter, Facebook, etc insofar as you're not violating their standards for objectionable/deniable content.
Freedom of the press does not mean freedom to use someone else's press as you see fit.