It is the balance between public sensitivities and the babies needs.
Any idiot can see that a baby's needs must trump the thoughts of those members of the public who may find discomfort.
Of course breasts have two funcious, but so too do many part of our bodies- our hands, our mouths can also be used for sexual activity.
Is that a problem for you too?
My grandfather was a racist bigot and found great discomfort in being on a bus or cafe if black people were there.
Should his feelings trump those of a black person's right to be there?
Some women may not breastfeed discreetly- for whatever reason, it's not for us to judge.
Should we have levels of discretion? Facing a wall, a nursing tent etc. If a nipple is not OK then is part of the areola fine? If some breast flesh is allowed then how many square cm? Maybe a chart on the wall could help.
We can't apply this nonsense of "discreet" breastfeeding. Far too subjective.
Sometime breastfeeding is not "discreet".
If you have a problem with that then get a shawl to cover your head when you are out and about.
Or even better stay at home.