I once disliked modern radio pop music, from Puff Daddy to Taylor Swift. But now that I have two young daughters, I think of that iHeartRadio junkfood music as made for kids, and suddenly it seems benevolent. Little girls, like my four and nine year olds, need their own music! And in that respect, I believe Katy Perry does a good job being a sort of kids-strength Beyonce.

My older daughter Cleopatra loves Katy Perry. So, I thought it appropriate to interview...