Guaranteeing people a decent retirement and decent health care does more than smooth out the rough edges of capitalism. Those guarantees give people the freedom to take risks. If you know that professional failure won't leave you penniless and won't prevent your child from receiving needed medical care, you can leave the comfort of a large corporation and take a chance on your own idea. You can take a shot at becoming the next great American entrepreneur.
The progressive argument for social insurance in a nutshell.