Carlson Grover is Uncle Sam on opposite day. He embodies all the critiques the novel wants to throw at government and bureaucracy.
We'd like to analyze this character for you, but he pretty much provides his own analysis for us, and it isn't pretty. Two quotes really sum up how Carlson embodies all wrongs of government:
Oh, c'mon. Can you ever "solve" poverty? Can you ever "solve" crime? Can you ever "solve" disease, unemployment, war, or any other societal herpes? Hell no. All you can hope for is to make them manageable enough to allow people to get on with their lives. That's not cynicism, that's maturity. (3.4.11)
[…] it means that, in politics, you focus on the needs of your power base. Keep them happy, and they keep you in office. (3.4.15)
One would think government's role is to fix those problems, but Carlson's attitude suggests this isn't the case. His counter is that politics is not about helping others but about keeping your job. Sure, politicians do help people—a select group of people, consisting of those who voted a politician into office. Obviously, this shouldn't be the case, and the biggest problem is that Carlson can't see that is attitude is indeed cynical.
Oh, in case you were wondering: yes, Grover shoveling dung while talking with the Interviewer is just a wee-bit of not-so-subtle symbolism.