All three of the programs you name are untouchable because they are funnelling money directly to powerful political stakeholders. Being real blunt here, poor people don't make political contributions and they hardly even vote. For the most part, they are easy political marks and cuts to general-population social programs happen regularly.
There are notable exceptions, like senior citizens - which is why we haven't done anything about the unfunded expediture on the Medicare prescription coverage.
While I won't discount your claim about hidden agendas behind much bureaucracy, I don't think you can really apply this to two of my three examples. For ethanol subsidies, sure. But it'll be much more difficult to make the same argument about the War on Drugs or the TSA. In these two cases, how is money being funneled to powerful political stakeholders?
Police departments and corrections officers of all types. The TSA is a giant jobs program for workers no one else will hire, and the body scanners are produced by a company owned by the Secretary of Homeland Security that mandated their purchase.
There are notable exceptions, like senior citizens - which is why we haven't done anything about the unfunded expediture on the Medicare prescription coverage.