pretty much everything could be "considered harmful" in some situations

what is really harmful is thinking that any one size fits all.

as for the "filter bubble" - thats a seperate issue that is also a problem in centralised networks. (actually worse there, necause most of those users haven't even thought about it and some of the might actually think the whole world thinks like what they see inside their bubble)

that probblem is more to do with the UI

It is much less of a problem when more of the discussion is organised around topics of interest (like traditional web forums, usenet newsgroups, etc) rather than around user profiles.

ie less about me me me and more about what I'm interested in.