[mikeash]

Yes, it's important to note that there are not people who are simply toiling away, objecting to the work, and reluctantly carrying it out. These are people publicly advocating for the organization, and trying to get more people to join it.

[gojomo]

Given that the NSA is likely to exist in some form no matter what, would an NSA with more fresh blood in it, of varying ages and competencies and ideologies, be more prone to abuse, or less prone to abuse?

You seem to be assuming that every person joining the NSA makes it worse, and that's not clear to me. In particular, a small, cohesive, monocultural institution will be more likely to commit abuses and more able to keep them secret.

[mikeash]

And you seem to be assuming that the NSA's abusiveness can be determined by the rank-and-file, when it looks to me to be completely due to orders from the top (up to and including the President).

So a good guy joins the NSA and tries to effect change. What happens? They tell him "no". If he refuses to carry out his job, they replace him and get somebody else. If he shuts up and works within the system and eventually reaches a position of real power, then refuses to abuse... the people with power over the NSA as a whole replace him and get somebody else.