> you suddenly read a comment
That phrase is hiding the real issue: on the internet, people engage with what they want to, and ignore what they want to. Attention, respect, engagement don't result from 'suddenly reading a comment'.
When there was only establishment newspapers and media they presented (what they considered) a balanced and responsible view. Now they've lost control of information and communication. Journalists dug deep to find a problem with the internet, and landed on 'the bubble'. The bubble is when people lack a balanced and responsible view...
There is just enough truth to 'the bubble' to keep the idea alive. On the internet it's easy to find radical information, and restrict your information sources to what you want. Back when everyone read the newspaper it kept public discussion narrowly focused [1]. Now we have lots of people who 'do their own research' and hold radical views. Also, the views that were suppressed under the establishment media are public and accessible to everyone.
There have always been people who live in their own little world, or bubble, but now it's much larger number. From the view of companies and social establishments that controlled the news this is a huge problem. From my view of society, I now sympathize with the US being a republic rather than a pure democracy, and I never thought that would happen.
[1] The smart way to keep people passive and obedient is to strictly limit the spectrum of acceptable opinion, but allow very lively debate within that spectrum..." -Noam Chomsky