I sympathized with that line of reasoning much more before reading Thoreau's Resistance to Civil Government. Now I'm convinced that he should either resign or be held as equally complicit [1].
http://thoreau.eserver.org/civil.html
[1] He should either be willing to defend the current system, or he should stop being its agent. Enforcing a law brings the same moral responsibility as writing a law.
Timely, in another thread we are celebrating Google for ceasing to be an agent of the Chinese government. We should never allow moral actors to absolve themselves of responsibility by pointing to a far-away law.
Plus if he resigned they'd just hire someone else. This isn't a position that would be hard to fill and he'd have accomplished nothing.
PS: I happen to pay a little extra taxes each year as a combination charitable donation and audit protection. As an added benefit I spend less time doing my taxes, but most people seem to dislike the idea. Multiply that savings across society and we would have both lower taxes (on average) and more free time.