I have been at multiple big tech companies when the stock dropped 20% or more. These events trigger a flurry of media coverage by analysts declaring that said big tech company's reign is over and soon everything will turn to crap (which it doesn't).
But this causes immediate concern among the employees because this directly affects their annual RSU compensation and it causes concern in the leadership because it makes them look bad and they tend to be the sorts that need to look good.
IMO don't underestimate what coordinated dumping of Facebook stock could achieve here. It does seem like a bit of a prisoner's dilemma though. After the initial price drop, the stock will recover because Facebook isn't going away anytime soon. So from a pure greed standpoint, don't sell. But that's not what this is about, is it?