Earlier quoted context omitted.
On the flip side of that, maybe you do want ex-NSA staff with the inside knowledge so you can protect yourself against their tactics. Isn't that the same reasoning for hiring ex-black hat hackers?
If someone is willing to divulge inside knowledge of his last employer you have to assume that in the future he will be willing to divulge your inside knowledge.
Sometimes employers are willing to take that risk.
Do you think Ed Snowden is now more or less employable now?