You are assuming the people in social media are a representative cut of people in the society but what you will notice quickly is that this is not the case, jus

You are assuming the people in social media are a representative cut of people in the society but what you will notice quickly is that this is not the case, just look at echo chambers. If I am trying to debate the same fact on a far-right or far-left post, undoubtedly both will come up with the same discussion and conclusion - let's not lie to ourselves. So for your claim to have any validity the requirement of a fair, unbiased group of people on all posts would need to be given (in the first instance, there are a lot more issues with this, just look at the loud people versus the ones not bothering anymore to comment as discussing seems impossible) and that is just de facto not the case and the reason fact-checking is indeed helpful.