With the recent U.S. Supreme Court cases allowing gay marriage, and the government never stopping people from getting married who couldn't have children, the last vestiges of the "marriage is for raising children" argument have gone by the wayside.
What is the government's interest in marriage?
What is stopping me from finding a poor college student, marrying him for the tax incentives (and him me for the health insurance), and breaking it off when it is no longer financially or emotionally convenient?
I ask from both a practical standpoint (can I do it) and a philosophical standpoint (if I tried this and it were challenged all the way to the supreme court, what would the likely out come be).