"to have a wet-nurse is unnatural and harmful"
In Emile: Or, On Education,
Rousseau put forward his belief that breastfeeding was better for the child than the practise of wet-nursing. He wrote: “but let mothers deign to nurse their children, morals will reform themselves, nature’s sentiments will be awakened in every heart, the state will be repeopled."
Employing wet nurses was common in aristocratic households across Europe as it was thought that breastfeeding inhibited a mother's ability to fall pregnant again quickly.
For more on Rousseau, see bookmark to page 21, "Contract social".