In this hour-long lecture, Ryan T. Anderson, of the Heritage Foundation in Washington DC, makes a reasoned case for opposing same-sex marriage on public policy grounds. He speaks rapidly and covers a lot of ground. But it is well-worth watching.

This event was videoed at Stanford University where he was a guest of the student-run Anscombe Society. His presence on campus generated a controversy because some students objected to his “hate speech”. 

It's a great summary of the main arguments. Watch it.