Why did Fer's Father feel that he was being foolish to let Fern raise the runt?

Fern's father believed that the runt would be useless in every way. He's giving into Fern's whim....... and he thinks that giving in is foolish because it gains him nothing. Well, nothing but the love of his little girl. What's so foolish about that?

Fern's father felt that the pig would not survive because it was a runt.