The thing is that people have tried asking why some (mostly men) are so bothered by a woman breastfeeding her baby in public, while not showing any breast or nipple (mom's tend to be quite discrete with the whole thing, covering up with a blanket even though it's often a nuisance)... And they really don't have an answer. "It's disgusting", "I bothers me", "I feel uncomfortable". Yeah, but why? Why is it disgusting, when you are feeding a baby its milk, from a body part that was designed to do so
So my thoughts are going in the direction that it has to do with the monopoly on women's sexuality that some seem to feel, perhaps even unconsciously so, and when they see sucking on their mom's breast they immediately find it disgusting... Because they do the same, but in a more sexual context....