Centuries ago, people were regularly convicted and executed (via various brutal means) for witchcraft.
if you look up the crime, you pretty quickly realise that it is basically an impossible crime to commit.
Convictions stopped, when Courts developed rules of evidence; in particular the hearsay rule. Essentially, rumours, gossip, and in this day and age, what an anonymous person spouts on the internet is not admissible evidence in Court, because of the hearsay rule.
Thankfully, in this day and age, if someone wants to make allegations (say hypothetically to take a current example) that someone witnessed voter fraud (just a hypothetical example as it appears to be a current topic), a Court would require testimony from the person who claimed to witness it, not second hand or third hand accounts from people who hear a rumour in the local town market place, or read it on the internet. This was a game changer, in terms of the conviction of witches, in the past.
The obvious problem with hearsay is that it can not be verified. The more subtle problem with hearsay is that it can not be verified by more and more hearsay. Larger and larger groups in the town market place repeating each other’s stories do not make those stories more true. Also, larger and larger internet circles repeating the same conspiracies in an echo chamber do not make the conspiracies more true.
Further, some of the vocal participants may have an agenda. To take another hypothetical example, a bad actor may spread stories that he or she has hundreds of affidavits confirming (for example hypothetically an election fraud) but never show them to anyone, even sympathetic media such as Fox News. Perhaps the bad actor has a hidden agenda, such as raising large amounts of money from the gullible? Perhaps we can detect the bad actor when he or she not only does not produce copies of such affidavits to the Courts, but does not produce such copies of the affidavits to the public either.
In this day and age, I am not concerned about the Courts or any modern country being fooled by such behaviour. What does concern me is that out in the community, where hearsay is still valid evidence, and there is someone with a loud enough megaphone with malicious intent, we are all at risk of the mob attack described by WH Audin, as Simon quotes above.