Because it's lazy to just assume newspapers are always wrong about everything. If we don't assume newspapers are always wrong about everything, we can assume they are sometimes wrong about some things and sometimes right about other things. That makes reading the news a fact finding mission. Discerning the truth from fiction is just part of life.
You started this thread with a claim of "I don't think any of the popular sources of information are trustworthy." That seems to be a position of default assuming they are wrong.
Saying that something is not trustworthy is literally saying it is not something that is able to be relied upon to be truthful. This means one should not assume the source is correct. It certainly doesn't mean to assume it is wrong.
