It's probably different if you have a family, but I have quit jobs over moral implications no problem. Most people have pretty flimsy morals and will do anything to keep the money rolling in.
How do you know how many people would quit? Even if 99% of the US would refuse to work for the NSA, the last 1% would be plenty for the job.
It's a systemic issue if we can't afford to have morals. In the US, It's not just a paycheck you lose with your job. Many benefits are tied to employment. It's hard enough to quit a job (for any reason) in order to take time to find a better one. If you're whistleblowing it's even worse, as that generally invites a long legal battle & having future potential employers reluctant to hire you...
Of course, seeing what happened with Snowden or even other whistleblowers more recently, like Suchir Balaji or John Barnett, makes it clear that more than financial security is at stake & acts as a chilling effect.
> It's probably different if you have a family
It truly is. I can’t emphasize this enough.
Most people have no safety net and if the money stops rolling in their life is effectively ruined for several years