I don't think that "non-robust" is the right way to look at it. Nor do I think that Facebook, Google, etc. have a large number of employees devoted to evil or that third party bad actors are fully responsible. I think what has happened is that the infrastructure is now based on algorithms that reward trolling and disinformation beyond the ability of anyone to stop. It's kind of like a gray goo scenario of the mental space of internet users that we're too anesthetized to really fight.