I don't see what the problem is in this case, honestly. Sure, it sounds silly, but they make a good point about the oddness of drinking the milk of another animal but being so apprehensive about consuming the milk of our own race... as nature intended.
The big problem though will be cost. Humans cost too much per hour to pay for milk production and still keep the milk at a reasonable price. By comparison, a typical woman only produces around a third of a gallon of milk a day... a cow can produce fifteen times that or more daily.
Everybody good, plenty of slaves for my robot colony?