Where Does the Government Draw the Line?

In my Philosophy class, we are reading a book written by John Stuart Mill titled On Liberty. You can read the pdf here. In the book Mill argues on what liberty and freedom means politically and philosophically. In the first chapter, he discusses the tyranny of the government summarized as the "struggle between authority and liberty" and "the tyranny of the majority."

I want to talk about the "struggle between authority and liberty" that Mill mentions. One of the concepts involved with the "struggle" is the Government's reasoning and jurisdiction of a law. Now, we frequently debate about Gay marriage as whether it should be legal or illegal. However, we do not debate whether government should even define marriage.

Where does the Government's authority draw the line? Should the government have authority in marriage, a traditionally religious institution? And if the government should have power over marriage, would that not violate individual sovereignty as it would limit one's personal choices?

These questions I ask of our CSP. Should we be arguing whether or not gay marriage should be legal, or should we be arguing whether or not the federal and state governments even have jurisdiction over marriage itself?