Earlier quoted context omitted.
Argument to Authority is a logical fallacy.
That logical fallacy always bothers me especially in cases where experience and inside knowledge are crucial to forming an opinion. The people listed above all have experience, knowledge and are more qualified to value companies than many other people. Of course it doesn't make their opinions absolutely correct, but it does lend some legitimacy to the FB valuation argument.
I've got a dot bomb crash, real estate bubbles and sub-prime mortgages that say otherwise.
No offence to any of them personally, and I'm not about to argue FB's actual valuation, but they all have a vested interest in making us all believe that it is as high as possible.
They are the last people one should be looking at when making an investment decision.