On no planet can you justify their 100B valuation based on their financials. Many people think facebook is a start up company with start up growth potential; its not a start-up growth company, its almost a decade old and its historical growth is pretty unspectacular in and of itself, nevermind its more current growth (or lack thereof). IPOs and specifically tech IPOs are cash-out liquidity events for early investors, not capital raises to fund future growth.
The other argument is "once they figure out how to monetize blah blah." They figured out how to monetize it a long time ago, that's why they have revenue and earnings in the first place. I do not understand what operational catalyst people are expecting where they're going to all of a sudden be able to produce massive sums of cash when they've been "monetizing" their use base for 5 years and have nearly flat earnings growth over the past year. Its not like they go public and all of a sudden all these giant companies are going to be like "wait wait wait wait, you guys have access to 900M people?! Why haven't we heard of this company before, we'll pay you a ton for advertising!"