Out in San Francisco, the Prop. 8 trial rumbles on. Following Monday's opening and Wednesday's dramatic Supreme Court reversal of federal judge Vaughn Walker's decision to broadcast the hearings, we'd imagine things will be pretty quiet, barring dramatic testimony, until the end of the trial.

But the whole affair has made us step back and think: why does the state regulate marriage to begin with? After all, marriages are at their heart private arrangements. Why aren't we able to head to our nearest Office Depot or Staples,...