You pretty much ticked off the whole list of justifications.
Millions of kids didn't see school until kindergarten, and somehow managed to socialize and build immunity. You think they stayed at home in their rooms instead of playing with the other little preschool kids in the neighborhood?
Few teachers are going to do a better job than a parent sitting in a chair and reading their child a book.
-teachers who know how to raise a child and how to develop them
There may well be cases where a parent is much lousier at raising a child than a teacher is. But that's a whole different issue than daycare.