[bena]

> And that's very useful for establishing which sources we should rely upon in a shared discussion.

Not necessarily. If someone doesn't like the dictionary, for example, then you're not really dealing with someone who is looking for actual information about the definitions of words.

Calling Breitbart a propaganda channel doesn't say anything except you think "propaganda" is a negative word and you don't like Breitbart. If you would instead have told him of the many times it promoted misinformation and conjectural outrage over substance and you don't feel like sifting through the chaff for any possible wheat so by default you don't treat Breitbart as a source of reliable news. That would be different.