Although you "paid" in you didn't really "earn" anything for those payments. Since you were not really buying something, you were being taxed by the Government to fund a benefit program.
I have always looked at it more as a forced savings account, which is more or less what it was intended to be. The actuality? Far different, sadly.
"A casual stroll through the lunatic asylum shows that faith does not prove anything." - Friedrich Nietzsche