If someone is perfectly content with what they're doing, then this is not for them. Simple stuff. But it's a near certainty there are people in there who are not content with what they're doing, who think it's varying degrees of wrong but keep doing it anyways because job, family, patriotism, whatever.
I would like to see our society stigmatize these kinds of jobs the same way an alcoholic is, FWIW. As in, if you're getting hired somewhere, having intelligence connections on your resumé is grounds for having it thrown in the trash.
You need not be a moustache-twirling Saturday morning cartoon villain to be complicit in perpetrating a great wrong.
And as far as brainwashing goes, you get wonderful things like this[1] being circulated in internal newsletters. It's bald-faced, pro surveillance propaganda designed to get those who it's intended for to stop thinking so hard about it.
[1]: https://edwardsnowden.com/2015/08/25/the-sigint-philosopher-...