Social security is a sort of retirement benefit paid out by the United States Federal Government. During your life, you pay into Social Security, and that money goes to right back out to the people currently receiving the benefit. Some people have the impression that you pay in, it gets saved up to pay you back later, and that's not true. You're paying social security for people right now, and in the future, the idea is that the people then will pay for your benefits.

Thus, any social security reform that allows people to invest their money, instead of paying it into social security, will deprive people of their benefits.

It was written into law around the time of the great depression.