The problem with a trading house like Mt. Gox is that some people assume that all of the players are altruistic (these "some people" being "me", somebody with a technical, non-financial interest in bitcoin).
What happened here is just natural selfishness: the person that executed this buy order knew that the market was crashing, and that something was going wrong, but decided to exploit it regardless.
Then trying to withdraw $5 million USD from Mt. Gox?
I guess it's just crowd psychology. "If I don't exploit this market, somebody else will!"
It's sad, and it's just my naivety showing here, but bitcoin looks like a nerdy sandbox from the outside (casually reading about it on HN); it's a place for crypto/economics geeks to play around with finance.
Of course it isn't, and the actions of this [very greedy] person demonstrate that.
So why do I want to use bitcoin? What advantages does it offer me over USD right now? Before seeing this crash for the last couple of days, it felt like the advantage was that bitcoin users were mostly geeks, and mostly trustworthy. The regulation that bitcoin is avoiding is starting to look pretty darn appealing.
How stupid/childish of me is it to daydream about a world where somebody saw this crash happening, did exactly what he did (or maybe put in the buy order at exactly $0.02), held the bitcoins until the crash ended, then just gave them back to the sellers at cost?