This is classic Krugman. He offers opinion as if he were stating fact. And he couches it in just enough Academia-speak that the casual reader will think that the statement MUST be true. I mean, how many readers eyes glaze over, when they get to "...proportional to the square of the number...", and think "I don't know what that means but clearly this guy must know what he is talking about."
I honestly don't know why he is so influential with so many people.