Yes, I agree. "Echo-chamber" and "bubble" are features. Having a informative and effective discussion at a high level, and having opinions moved, predicates a high degree of common ground.
Effectively challenging somebody's worldview doesn't begin with "everything you consider true is false, now listen to me" as is sometimes the preferred method of radicals. Being bombarded with information and viewpoints you consider wrongheaded doesn't expand your horizon, it galvanises you.
But when a person I have a lot in common with and agree with on many issues says something that I don't instinctively agree with, I listen and at the very least make sure I understand the full argument before I decide whether I think it's wrong.
An echo chamber fosters confidence in a single perspective, or a small subset of many perspectives. And not everything we speak about is mathematical and can be formalized so that we can have confidence in a single perspective (social, political issues).
Can you, in particular, handle being confident in one perspective and being able to acknowledge, understand, and evaluate another? Maybe. Can most people? I don't think so.
"Having a informative and effective discussion at a high level, and having opinions moved, predicates a high degree of common ground."
We can agree on definitions, but that's not necessarily an echo chamber. An echo chamber, or the negative kind of echo chamber, is when a (nonmathematical, nonformal) perspective or conclusion is reinforced by the entire community.
Example: "everybody has the same opportunities and therefore everybody is equally capable of achieving success". You get people on hacker news asserting this all the time. This is not a definition. This is dogma.
"Being bombarded with information and viewpoints you consider wrongheaded doesn't expand your horizon, it galvanises you."
Key phrase: "[ideas] you consider wrongheaded". Nobody has all the right ideas from the start. A priori, there is no reason to think that you will never encounter any ideas which appear wrongheaded to you at first.
Effectively challenging somebody's worldview doesn't begin with "everything you consider true is false, now listen to me" as is sometimes the preferred method of radicals. Being bombarded with information and viewpoints you consider wrongheaded doesn't expand your horizon, it galvanises you.
But when a person I have a lot in common with and agree with on many issues says something that I don't instinctively agree with, I listen and at the very least make sure I understand the full argument before I decide whether I think it's wrong.