从道德上看
some people object to wet nursing because they have mistakenly equated breastfeeding with sexuality and eroticism
你可以认为这种看法没必要，但是很多人就是这样看。而且在欧美，双方经济地位不像中国差别这么大。

从科学角度看

Currently, the La Leche League discourages wet nursing and cross nursing because

* There is a chance of transmitting disease in the breast milk
* The composition of breast milk is different depending on the age of the baby. Thus a wet nurse with a 6 month old child will have milk that is best for a 6 month old. This milk would not be optimal for a newborn.
* The birth-mother’s milk-supply will decrease if she gives the baby to someone else to breast feed. This is especially true in the case of multiple births.
* The mother and baby will not experience the special mother to child bonding that occurs during breastfeeding.

其实最后这一条也涉及道德。