Here's the thing. There are these things called breasts. They are body parts. They serve many functions. Sometimes, they feed babies. That part is pretty important.
When a woman is breastfeeding, she is not trying to offend you with her breasts. She is giving life-sustaining food to her child. Do you really want her to have to do that behind closed doors — especially if those closed doors are the doors of a nasty public bathroom stall?