... Also, if he's an arbitrager, then why would he want to calm people down? A stampede would be perfect for him since Gox' bitcoin price would inflate further...
Ya don't kill the goose that is laying the golden eggs, ya know.
How would the goose die?
If, for reasons which remain mysterious to me, there is a comfortable and stable gap between Mt. Gox and others, and if one has a relationship with Mt. Gox which allows the kind of turn-around needed to succeed at arbitrage, then it makes the most sense to try to just keep the happy state of affairs chugging along. A 'stampede' at Mt. Gox would probably spell it's flame-out and thus the end to the milking the arbitrage.