These outright falsehoods that people take for truths are not taken for truth in a vacuum. As cliché as this may sound, people want to believe these things. So they believe them.
I was reading somewhere that people tend to readily assimilate information conforming to their own world view, and have a tendency to block out information that does not conform to their world view. It's claimed that these tendencies pre-date the internet.
If that's true, the negative effects of virality were inevitable.