Breeders always assume people think it's inappropriate because there's an exposed breast.
I don't find exposed breasts inappropriate. Not wearing a bathing suit top if you don't feel like one is perfectly acceptable in most of Europe. It's not about the breasts.
Nor is it specifically about the function. Breastfeed if you like. I don't give a fuck, provided the bodily fluids are contained and I'm not exposed to them. I was breast fed as a baby, but somehow no pictures of this made it in to the family album.
Taking a picture and posting it, however, is deliberate provocation. It's insisting that others must be not only accepting of breastfeeding as a way to feed a baby, but must laud the very process. Why should we? I wasn't present and didn't want to be when the sperm donor blew his load, and I feel the same way about this biological function. The persecution beefers complain about reminds me a lot of the persecution Christian extremists complain about. If someone isn't kowtowing to them they're the victims. They're not content with someone else taking a "live and let live" approach, instead they have to push it in everyone's faces.
That discomfort you see on my face is embarassment on your behalf, because you're clearly a shameless attention whore incapable of cringing at your own pathetic demands for attention. (That's assuming you're far enough away...if you're nearby, I'm thinking the same thing I think when I see a junkie shooting up in public transport: namely, I sure as hell hope no bodily fluids splash on me.)