Depending a bit on your viewpoint, social justice, social decency or even a self-interest in a stable society lead one to a safety net.
Destitute seniors and children impoverished by their lack of ability to provide for their own income or impoverishment of the able by being singled out by disease in the lottery of life or severely injured in the risks of an active life are outcomes that we've agreed we should pool our resources as a society - through government - to provide assistance to the afflicted - the safety net.
Just as what today passes for health insurance and is not (see here for a discussion by Megan McArdle of Catastrophic insurance versus soup to nuts plans), but is the implementation of the progressive base's desire for massive redistribution and as little cost sharing as possible: e.g. the idea that you show up at the doctor, get treatment and no one hassels you for or even mentions money all paid for collectively through the federal government.
The safety net is to the current welfare state as catastrophic health insurance is to Obamacare. Redistribution beyond our ability to pay for it in Social Security, Medicare, Medicaid, Obamacare and a hundred other programs (think Veteran's Administration, Native American Healthcare) are bankrupting our treasury and, through dependency, our self-responsibility oriented moral philosophy.