I know that; you forgot two things;
it is designed to take advantage of the net gains realised with an increase in productivity which is what drives the whole program.
As productivity per man hour increases it covers the shortfall in contributions.
And the increase in value added asset acquisition; ie interest on investments.
Social Security works like any insurance policy works; just like your car insurance policy.
The powers that be want you to focus on the two simplistic arguments while disregarding the real concept behind the program.
That still doesn't answer the big question which is what you plan to do with those who don't or can't save enough to support themselves in retirement. Do we let them starve?No; we impose hienous taxes on those who have saved to pay for their retirement to salvage the less able ones. Thats what is going to happen.