Social Security is welfare. The amount you receive is generally much, much higher than what you pay in.
Conceptually, at least, Social Security is supposed to be an insurance policy, not welfare. The idea is (or, rather, was when it was first implemented) that people might and do live past the average life expectancy. Such elderly people may no longer be able to work to support themselves, so they get to cash in on an insurance policy against getting too old. If there's a flood in your community where it rarely floods, and you have flood insurance, you'll probably collect much, much more than what you paid in. Same with fire insurance, etc. That's the nature of insurance. And Social Security is supposed to be insurance against living past your life expectancy.
Why did we need this insurance? Because even by the 1930s when the system got going, communities were starting to fragment as people became more mobile, No longer could grandpa depend on his children (or even his community) to support him when he couldn't work any longer. The Great Depression resulted in even greater problems with elderly people not having enough to survive; hence a massive "group insurance policy" to help out those who lost the gamble and lived too long.
But now, instead of life expectancy being about 65 (as it was when the program was started), now it's almost 80. So the vast majority of people are being awarded a decade or more of their "insurance" for living past their expected lifespan. It's sort of like a flood insurance company that insured only one area, and due to dams and other developments, that community became a flood plain. Pretty soon that insurance company wouldn't be able to operate -- it would be paying out to everyone.
Social Security was never intended to be a retirement plan, nor was it intended to be welfare. It's a broken insurance system. (People should pay attention, since the same problems with Social Security are destined for the national health care regulation when it goes from an insurance system to simply a distribution system, like Social Security has.)