For pretty much every online community starting from the smallest web forums, you need an ability to remove unwanted content and people from that platform. Even platforms for very free, unrestricted discussion need to fight commercial spam and simple vandalism. The ability to have a community of group A for topics that interest group A requires effective moderation, i.e. the ability to remove unwanted topics and people from that forum, blocking them
before the majority of the group have had to encounter that unwanted content, otherwise you have a very, very poor experience full of spam that kills the forum, and
that is very relevant from a practical standpoint.
For some of that content the proper answer is "go have your community somewhere else"; for other content (e.g. penis enlargement spam and people who post it) there probably is no community that wants them, and for that freedom of speech consists of being able to freely speak on a soapbox somewhere where all the 0 people who want to hear you can do it.