Many CIA agents when working overseas have official covers with the US government. This gives them a great degree of protection. If they are caught, they have diplomatic immunity, and get shipped back to the US.
If you don't have diplomatic immunity, Like Mrs. Plame, they face another reality.
On a recent Sixty Minutes story Ed Bradley made this observation.
a NOC who was caught spying in Shanghai in 1951 and died after 19 years in a Chinese prison. To this day, the CIA denies he was an agent.
In addition, the decision by Libby, Rove, Cheney, Bush to expose Mrs. Plame also exposed any contacts she used as potential spies for the US. It also exposed a CIA front company. Any other CIA agents using that company as a front were also outed as spies, as were all their contacts.
We have no way of knowing if this act of political assault may have resulted in the arrest, imprisonment, or execution of people who had been trying to help the US control weapons of mass destruction, but to think that it could not have happened is naive.
A better review is avaliable at The Ostroy Report.