Social Security turned 75 last week. It should have been a joyous occasion, a time to celebrate a program that has brought dignity and decency to the lives of older Americans.

But the program is under attack, with some Democrats as well as nearly all Republicans joining the assault. Rumor has it that President Obama’s deficit commission may call for deep benefit cuts, in particular a sharp rise in the retirement age.

Social Security’s attackers claim that they’re concerned about the program’s financial future. But their math doesn’t add up, and their hostility isn’t really about dollars and cents. Instead, it’s about ideology and posturing. And underneath it all is ignorance of or indifference to the realities of life for many Americans.

About that math: Legally, Social Security has its own, dedicated funding, via the payroll tax (“FICA” on your pay statement). But it’s also part of the broader federal budget. This dual accounting means that there are two ways Social Security could face financial problems. First, that dedicated funding could prove inadequate, forcing the program either to cut benefits or to turn to Congress for aid. Second, Social Security costs could prove unsupportable for the federal budget as a whole.