There's a thing I do not understand, nominally speaking French banks' exposure to Greek debt is not that large. I have not a easy link as reference, but I seem to remember reading in some of last week's FT editions that BNP Paribas had the highest exposure, with ~4 billion euros, followed by Societe Generale, with 2 or 3 billion. Of course that to you and me it looks like a lot of money, but the Kerviel case alone cost SG almost 5 billion euro in direct losses (not counting the losses incurred by the case on the share price), so Greece going down (or taking a 50% cut) shouldn't be that much of a tragedy, at least in theory.
Now, why then all this panic? It could because of what you said ("spread rumors, accumulate riches"), or because there's a hidden iceberg somewhere in these muddy waters: maybe countries like Italy and France are much closer to collapse than people think.
Maybe it's because other countries could follow the same path. Greece isn't that big but if the other PIIGS fail to pay, it could be much more than a few billions.
Now, why then all this panic? It could because of what you said ("spread rumors, accumulate riches"), or because there's a hidden iceberg somewhere in these muddy waters: maybe countries like Italy and France are much closer to collapse than people think.