In my experience there are more conservative echo chambers than progressive ones, but they function the same way. And personally I don’t believe there is any such thing as an inverse of politically correct, any more than there is such a thing as “reverse racism”. Racism is racism no matter what color or ethnicity you discriminate for or against, and political correctness is political correctness no matter your politics*.
I don’t care for echo chambers regardless of what the filter is. Others obviously feel differently, given how increasingly divided and polarized we are becoming.
But here’s how you can tell an “echo chamber” effect from other styles of forum moderation.
When posts are removed and users are banned because people don’t agree with them, or because appropriately mimetic memetic invocations have not been observed, it’s an echo chamber.
It’s not necessarily an echo chamber if posts are removed because a user has dragged in extraneous, disruptive issues (“de-railing”) or because someone is using argument styles that are not permissible on the site (ad hominem comes to mind immediately) or because someone is in some other way ignoring site guidelines that are intended to promote the conversations the site wishes to enable.
I’m involved with a number of interest groups where politics and religion simply are not allowed. Online, any post that mentions either is deleted; in meatspace, any such discussion meets immediately with social disapproval and peer sanctioning. That works remarkably well when the subjects of discussion are tightly and specifically focused, such as bladesmithing or electric vehicles, but very poorly in wider fields. You can’t discuss history without discussing religion and politics!
Edit: was it Bronofsky who said “politics is the systematic organization of hatreds?”
Edit2: No, it was Henry Adams.