Facebook should trade for what Facebook is trading at at the moment in time Facebook is trading.
The end.
The end.
"This company is trading at this price, which is appropriate because this price is what the company is trading at. My recommendation is to purchase shares in this company then sell them at a higher price later on. Alternately, we can short this company's stock, and then profit when the price falls."
The GP's comment reminds me of the famous Bill Parcells quote: "You are what your record says you are".
If I purchase stock in a company one week at $33/share, and the next week that same stock is trading at $23/share, it is highly unlikely that the stock was worth what I paid for it, unless something unforeseeable happened to that company during that week which dropped its value by nearly a third. Market capitalization is only an estimate of real value. The only reason the stock market tends to do such a good job of estimating it, is that so many people are doing their homework before deciding to purchase a share.
Articles like this and discussions like this are critical to a healthy market. They help people decide if they should buy or not, and so they promote market efficiency and accuracy.