Carefully moderated... echo chamber
Why equate one with the other? You can have a completely unmoderated or poorly moderated echo chamber. Conversely you can have a carefully/poorly moderated or completely unmoderated communities that aren't echo chambers.
The concepts are orthogonal.
In fact, I'd argue that completely unmoderated communities are the most likely to end up as echo chambers. Because only those with extreme views would stick around so the natural end state is a community of extremists. Example: 8chan