This list has been the focus of heavy criticism since its publication in 1991. According to Wikipedia (https://en.wikipedia.org/wiki/Cultural_universal), the scholarship was not up to scratch. 

As it happens, there is an answer to your question about why God would kill the firstborn of the Egyptians -- even if they were babies. I know this because I asked this very question during the time set aside for asking questions in during the Seder, the year I was (maybe?) fourteen. We always drove to Chicago for the Seder, every year, and stayed for several days. My uncle, source of biblical truth for the (large) extended family, gave it to me: "Bad blood," he said. "It doesn't matter if they were babies. They were going to grow up to be Egyptians. The sins of their fathers are in them, and they will do what their fathers did."

I never went back.