Landy's last act

I don't know what it's really like in the CIA, but my guess is that it's a balancing act between doing what's effective and doing what's legal.

A covert action group can certainly thrive in secret doing what's effective but illegal with the right political cover, but that cover is only good until the op is exposed. You will have people griping about whistleblowers endangering national security, but if what they were exposing was illegal the covert action people and anyone providing cover is suddenly exposed to at a minimum a ruined career and at maximum, prison.

What surprises me, though, was how easily Landy was able to get away with faxing the documents. What would have prevented David Straitharn's character from just shooting her on site and claiming she was aiding Bourne, prima facie guilty of treason and that killing her was an urgent matter of national security?

Sure, once the documents are disseminated and its known she disseminated them, she's generally safe. But there seem to be a lot of whistleblowers who end up dead or discredited because they didn't get the right evidence to the right people in a timely fashion.

Landy was in the dark about Treadstone and all of the dark money that organization was making outside of the CIA's initiative of advancing/protecting American interests and assets. If you're talking about the overall mission of the CIA as an organization that will do whatever it takes to secure American interests above the welfare of foreign countries, foreign peoples, and in some instances American lives.

I never read the book so I'm not sure if she's part of the adaptation or written in for the movies, but I didn't feel a sense of shock that she would spill this information to entities outside of the CIA and with the power to expose them. It's not like this hasn't happened in real life either.