Bereishis 1: Let there be... curses?

Rashi on 1:14 says that the reason why the word m'oros, lights, in the section about the 4th day of Creation is written without a vav is in order to allude to the word me'eira, curse, since the 4th day of the week is a day upon which young children are especially susceptible to the disease of askera, often translated as croup, as is brought down in Sofrim 17:5 and Yer. Ta'anis 21:2. Why is this special characteristic of the 4th day of the week given such importance that it alone of all of the phenomena of the days of the week is singled out in this central chapter of the Torah?