The value of a company in a fair market is a function of the confidence of investors that someone in the future will pay more for the same stock.
For a highly profitable company like Facebook, this isn't a foolish confidence in anyway. Even if you don't like Facebook it would be a very radical position to take to think that their profits next quarter will be remarkably lower than this quarter.
In greater fool theory, you know there is no reason the investment is going to increase in value. You are just hoping someone else is going to buy from you and accept that risk too.