I think it's fine provided that the child doesn't have teeth, and the mother attempts to be discreet. I only feel akward when people are obviously being immodest about it. It's not that hard to cover up with a blanket, or if you don't have a blanket to use a change room or restroom.
I'm not clear why a child having teeth has anything to do with this? Some babies start growing teeth as early as 3-4 months and some not until a year. This has nothing to do with whether it is developmentally and nutritionally appropriate to breastfeed. And you'd be surprised about a blanket... once a baby is 4 months or so, very few babies will tolerate a blanket or cover of any type. The whole point of breastfeeding advocates, is that there IS nothing immodest about breastfeeding. Restrooms are unclean and an inappropriate place to feed ANYONE, much less a baby with a developing immune system. Personally, I feel that I am as "discreet" as I can be with my infant. If someone doesn't want to see my baby breastfeed, they don't need to look. If someone wants to stare at me breastfeeding long enough that they might see the flash of a breast when the baby gets on or off, then they are the one with a problem and no manners, not me!