What is the ideal role of government?

What is the ideal role of government? What parts of the economy should government never touch? Through the government, citizens are provided health services with Medicare and a financial safety net through Social Security during their retirement. Should the government be providing these services? The public sector has grown while the private sector has shrunk due to real economic conditions. How can the government be more aligned with its taxpayers? What are the advantages and disadvantages of libertarianism?