The following link is a page regarding the history of SSI and how and why it came into being. http://www.ssa.gov/history/briefhistory3.html
Before 1937 there were charitable churches just as there today which helped but the grow of this nation and directly related to the Civil War the need for orphans and widows were great and more than churches and organization could support. What happen in the depression was a wake-up call to set something up to assist this nations' elderly. That's was the intent of SSI, not what it's become, or how it's been used.