The article in question is here and there's another article discussing the issue here. I don't think they're really saying that breastfeeding is unnatural – they're saying that "natural" is a loaded word.
Apparently there was a UK paper arguing that natural was a "mushy" word and considering whether it's time to get rid of it, which seems a bit Orwellian in itself. Who decides when it's time to "get rid of" a word? Language can be used as propaganda. But the UK paper discussing this appears to have been removed.