Of course many federal agencies have no justification whatsoever, and exist only to pander. The issue is somewhat more complicated than that however, as there are agencies that do have legitimate functions were they not so ineptly administered:
CDC - I can agree with the existence of a federal agency that coordinates epidemiological research, reporting and response, rather than such research being conducted independentaly in 50 states, with no agency monitoring the regional spread of various contagions. The problem is, they spend an inordinate amount of resources tracking *epidemics* of "gun violence" and second hand smoke and attempt to influence policy and legislation.
FEMA - somebody needs to coordinate responses to disasters that exceed the capabilities of local and state authorities. As long as they are coordinating Department of the Interior, Defense etc. assetts in response to a disaster, fine. When they start handing out cash cards for bling purchases in New Orleans, they've stepped into the twilight zone.
NASA - A lot of what they do should be turned over to private industry where it would get done more cost effectively and rapidly. Space should be viewed much as the Louisiana Purchase was during the time of Jefferson, Lewis and Clark, but this does not mean NASA should be done away with all together.
I could give you a number of other examples, and while we agree government is entirely too large and has many components that could be done away with yesterday, there are more that are legitimate in concept, but not in practice. To paraphrase, Dilbert cartoonist Scott Adams, I'm not anti-government; I'm anti-idiot.
We are still suffering under the legacy of FDR’s socialist regime.