I think there are other factors, not taken into account, that substantially modify these calculations.
1.-You can spend several times the same safecoins until the network begins to suspect that something bad is happening. How many times? It will depend on many factors (number of potential buyers, velocity of circulation of the safecoin, etc…).
2.-The benefit of the attacker, who controls a section, would be a lot greater going short against the safecoin than selling the coins of that section. Using leverage, these gains could be huge.