> Except when it is. Given sufficient downvotes, a post will fade to the same color as the background, making it easy to scroll past and not see it.

It doesn't change anything. The content is still available for anyone to see if they want to.

Censorship is about making content unavailable. Not giving the exact same visibility to everything out there isn't censorship. Or upvoting is also a form of censorship, since it moves content above less-upvoted comments making less-upvoted comments more likely to be missed by people who won't scroll to the end of the page.

And for anyone used to HN's way of doing things, it's not hard to spot faded comments and highlight them if they seem of interest given the context around them.