Previous generations had the Nazis and then the Soviets as the 'enemy' and they were tangible opponents. Potential whistleblowers might have been able to convince themselves that they were acting for the greater good, and kept themselves quiet.
The new 'enemy' are the terrorists, and they are neither particularly tangible or visible. It is not so easy to convince yourself you are acting for the greater good in these circumstances.
In actuality, the reverse happens. Snowden's patriotism convinced him that the actions of the NSA could not be justified as 'greater goods', and so he became a whistleblower.