filter bubbles are created by social media corps using algorithms to systematically feed people content that maximizes ad revenue by keeping them hooked on the facebookian skinner box. someone choosing not to see something is not a "filter bubble."

Like I cannot stress this enough, the key bad thing about filter bubbles is that they're invisible, involuntary, opaque, and exploitative; you don't know what choices are being made for you, and they're being made to maximize your value to the corporation. Facebook doesn't filter content to protect its users or to keep them from being challenged, in fact it deliberately feeds them upsetting content that generates outrage/rage clicks.

This was, immediately and entirely, oversimplified into "Facebook keeps people from talking/hearing people who disagree with them." This is not what Facebook does! What Facebook does is feed people the content that will maximize engagement and keep people hooked on Facebook specifically. It will avoid, for example, giving you too much content you might like from a single source because you might leapfrog Facebook and just start reading their website instead.