Further proof that the absurd run-up in November when bitcoin reached $1,200 was illegitimate.
...so, then where was this cache of money that was destroyed to inflate the price? It would have to be a pretty large quantity to have such a drastic impact.
Occam's Razor to me suggests the answer is obvious: The vaporized deposits of MtGox users are the most obvious large cache of money, large enough to cause such a run up.
The next question is, who would do this, and why? The answer suggested by Occam's razor would be "Someone who could modify the MtGox database to create nonexistent fiat currency, but could not (or did not want to) create fake MtGox bitcoin holdings." This is because a person with this power would have reason to trade the "fake fiat" with legitimate bitcoin holders to generate bitcoins that can be leeched out of the site, and this would certainly cause the price to rise.
This doesn't answer however whether it was an inside or external party, I could imagine scenarios both with or without inside actors that would lead to this kind of activity. (Though I'd put my bet on internal fraud, based on the fact that so much effort was put into hiding the fraud and extending it over a long period, as opposed to going for quick profit.)
In other words, the situation at Mtgox was the opposite of what you describe: it had a lot of FakeBTC, bit its USD reserves were mostly real.
The modern day bitcoin trader should carefully consider whether they want to be a part of a market where the largest actors aren't bound by the rules they set for everyone else.
In this case, however, only some parties knew that MtGox's internal accounting was broken. Therefore, the price run up may have been "illegitimate" for a limited time period based on this asymmetry of information.
You are right though that over the long term a market price is always "legitimate" by definition, because of the maxim "something is worth whatever someone is willing to pay for it."