I once saw a really sad episode of Law and Order where a young mother had starved her child to death because she wasn't able to properly breastfeed but whenever she went for help she was told to not use a bottle but that "breast is best". Knowing that these shows are often based on true stories, I found it to be probably one of the saddest episodes that they ever had.

There is definately a fanatical fringe that has a zero tolerance for bottle feeding. You just need to come up with a snappy comeback that will leave them so shocked that they'll stop bothering you.

I don't know, maybe something like, "breast feeding will infect my nipple ring"