Back in my 30s I proposed on the Fool a plan where the Feds could keep my employer's half of Social Security. I would forego that and all my future benefits. In exchange I would be allowed to take what I contribute to SS every year and park it in an index fund.

Had that plan been enacted...I'd have about $3 million when I hit 65 and more when I hit 67. I'd be able to live 3x< better than what Social Security would have provided. So let's recap: I invest roughly half of what's been paid for my "Social Security" and I would still be 3x better off.

Whoops.

Sure, because you're positing that you would get solid, good returns on your investment. Which, being a Motley Fool user, you probably would have. It's a population self-selected for pretty solid financial literacy. So you end up with a really nice theoretical portfolio as the "privatization" side.

The problem with this proposal is....what if you hadn't? What if you had lost all your money, instead of getting X times your money? If you hadn't saved it, if you didn't put it in an index fund, if you had put it all in WebVan or Pets.com stock or lottery tickets? You can say you'll forego all your future social security benefits, but then you're a destitute elderly person who still needs stuff. You still need housing, you still need food, you still need clothing.

The whole point of Social Security is that it's supposed to ensure that seniors have a certain minimum income in their elder years. That they don't fail to save, that they don't invest in things that get zeroed out. That's why it's very much not structured the way you're imagining it, as if it were a personal retirement account with a rate of return. It's a federal social insurance program.