If a journalist phones a couple of sources, hears from them the same thing they are seeing somewhere and publishes that information, then the fact-checking has been done once and reaches thousands or millions of people.

If the way the information is disseminated requires those thousands or millions to do the fact-check themselves using the same process, then that is entirely impractical, which was my original point. Crowdsourced fact-checking is always going to be less reliable and exponentially more work than properly verified broadcast news sources. Even if many of them share their fact check, we have plenty of data to suggest the reach of that correction will be much smaller and it will still require a lot of private effort to correct the original info.

Sure, but would it not be better if they had also just cited the transcript of their contact with those sources? I understand that the news outlet can just fabricate a source, but at least a source will give readers an official starting point for investigation rather than just blind continuous skepticism. I'm of the opinion that a sketchy source is better than no source at all.