Breastfeeding your baby is wonderful, but it doesn't make you an expert on all areas of child-rearing -- in the same way that masturbating is fun, but doesn't make you an expert on sexuality. All you're doing is providing a bit of biological fluid and feeling better about yourself. And it's offensive to fling your fluids at others who didn't ask for it. Which doesn't stop some mothers from screaming as if every bottle was bursting with Bane Venom.
For self-secreted experts in all human biology, they don't seem to understand that people are different. Some people don't breastfeed, or can't breastfeed, for any of an array of reasons far too personal to get into with someone who's decided that "Mother feeding their child" is a valid target for public attack. There are orc tribes sneaking up on hobbits with better ethics.
"Look, I know that you have your own experiences, but I'm just awful, okay?"
Breastfeeding and formula are the ultimate human success stories. We've got our original method and the technologies we've invented to be better than mere nature. Which is the point of technology. The secretion of fluid from mammary glands isn't the ultimate level of natural nirvana; it's a pre-installed function of some tits. Most monkeys can do it. Not even every monkey, because bodies aren't born perfectly. But what makes (most of) us better than animals is that when someone's body behaves differently, we don't shriek and hurl shit at them until they're driven from the tribe.
The Alpha Parent
I'm all out of bullets in my "Be a reasonable human being" gun, too.