It is stated in chapter 1 that the demons hide themselves in a human heart, and are kicked out once the hole in the heart is filled.
However, in chapter 3, it is stated that they only hole themselves up in the hearts of women, because they will be born as the woman's child.
But in the majority of cases, they'll find love at some point before the child is conceived, so the demon would already be kicked out. So what's the point of artificially banishing all of them beforehand with the MC?