Nursing tops make it very simple to nurse discreetly in public. There are also many nursing blouses, casual shirts, sweaters, dresses, etc. that look nice, are comfortable and make nursing discreetly even easier. My favorite company for high quality, good looking nursing clothing is Motherwear.
I have had problem with shirts from Motherhood, such as difficult to use design for nursing openings, thin and transparent knits, and uncomfortable fabrics. Perhaps you will disagree with me about their products. They are less expensive than Motherwear which was the reason that I purchased them. I ended up so unhappy with them that I went out and bought more tops from Motherwear.
Even regular shirts can be used and moved in a way so that nursing can be done discreetly. I don’t think there is a need to expose an entire breast (although I have seen that done).
I know that many preteens, teens, and grown women wear shirts and bathing suits that reveal a lot more skin, or are tighter and let us see their entire breast anatomy (without even showing skin). I feel that babies should be able to nurse in public--absolutely. I also feel, though, that nursing mothers should nurse discreetly whenever they are in the presence of other people, such as in their own homes (and guests are visiting), at other people’s private homes, and in public places. It is a matter of etiquette and social graces.