Facebook was one of the main tools that allowed trump to win. That is some value right there. How much money would a government or a company spend to control people? That is kind of what facebook is allowing people to do.
If FB is an industry on the level of TV or radio, then it's almost certainly not overvalued.
The implications and consequences of the consolidation of this power and influence into one company is a different discussion entirely (and an important one).
1. Much more precise user targeting
2. Direct feedback on effectiveness (did the user click-through or even just linger looking at the content?)
TV and radio seem like very crude tools in comparison.