home mortgage interest deduction?

California's Proposition 13 property tax law.

Much of the special exemptions relating to health care and insurance which effectively tie it to employment, while restricting the ability for other groups to form for pooled risk. Addressed somewhat under Obamacare.

Big Ag subsidies.

Patent and copyright laws.

For instance, Detroit has created pension obligations that it cannot possibly make good on, and is having some difficulty dealing with those as it is bankrupt. Many other local governments have similar programs, but are not yet bankrupt.

Surely Social Security wasn't meant to be the biggest item on the Federal Budget. I suppose you can argue about its popularity, but it has become enormous.

Would you mind mentioning any one thing which federal government does which should be more costly than providing a livable income to everyone over the age of 65?

Our Federal Government is not responsible for most of the major functions of governance because our states cover most functions. Also, we aren't at war with a major foreign power.

Prop 13 in California