We call it differently because its purpose is different, not its actions.
No, freedom of speech is not censorship, no matter how hard so many try to push the idea. Censorship involves the use of force, be it direct or implied, not others choosing not to give you support. Inherent in the right to express an opinion is the right to not express an opinion, both yourself and on your own private forum. Hacker News (or any other private site) are not public forums, the public forum is the internet. If HN wishes not to allow certain things, that's literally freedom of speech. Of course, those choices can in turn be criticized (both here within rules at HN's choice but also on other forums entirely or by creating your own), and the criticism criticized in turn and so on. Depending on the arguments made and social and economic pressure it creates some involved may change their stances, or not.
But none of that is censorship. Censorship is the death of that process, force being used to put an end to the circle of social/economic discussion.
>That's why it's so tough to find the right balance between fostering a community and extinguishing it.
It's hard to do so sure, but not because of some "censorship" thing but just because managing human relationships and networks and community is hard.