I was going to make an "academic"-type counter-argument that not even terrorism fears approach the anti-communist hysteria that probably drove this incident, thus it won't happen again... but then there's the NYPD mosque spying case. It's not the same active blackmailing situation. But I think we can say the fact that it happened at all in "our enlightened day and age" is sufficient evidence that, if there were a few person(s) to discredit in order to tear down movements that the government didn't like or feared, they wouldn't mind trampling civil liberties to get it done.

Are there recent, well-documented cases of government blackmailing like this?