Let's take person who is 20 years old and use the assumption that they make $30,000. The amount of payroll tax that is being collected is $310 monthly. Half from their employer and half from the employee. To ensure we don't overestimate our final figure, we'll also assume that this person never gets a raise. They make $30,000 their entire life.
Over the course of the next 45 years we take that $310 and invest it monthly in a good mutual fund that averages 10%. At 65 their money would be worth $2,941,759. If you took just 1/3 of your balance and put in a good annuity, that would be roughly worth around a $14,000 monthly payment. A social security payment would be a fraction of that. It's a terribly inefficient system.
There are gives and takes for both parties. For the government this would help with the solvency of social security at the expense of income tax receipts. For me, I would gain tax free growth at the expense of future social security payments. There would obviously have to be limits on how much could be converted, but this is an option I'd be interested in.
From your post it sounds like you think we should never do anything because it can't benefit both parties equally. I think that's wrong. I also think that most people agree that social security is a disaster and reforms need to be made.