Uh, what?
Wouldn't this 'FixIt' program be signed too? (And if not, it would be trivial to do so).
Regardless, this MITM attack isn't exclusive to TOR, it's just as feasible to do with with regular internet.
Furthermore, I wasn't aware that you can mark exit nodes as "BadExit". That's a pretty cool feature; one that doesn't appear in the regular internet.
The story implies that TOR is dangerous - but as far as I can tell, it's actually safer than regular internet.