I believe rayiner's point is that infants can thrive on formula milk as well as breast milk. Please don't mock parents who choose to formula feed; there are many cases where it is preferable and/or necessary, just as there are cases where it is necessary to use antibiotics to supplement the body's immune system.
Remember, the couple of generations of Americans grew up on formula feeding. Breastfeeding rates were down to the 20% range in the 1970's. Yet, there is very little evidence showing any long-term negative impact in those generations.
And where have I done that? Formula is a fantastic invention that can specifically assist in very difficult situations.
But just as it is clearly inferior to take antibiotics daily because it is too inconvenient to wash one's hands ... so to is it clearly inferior to use formula when the mother is capable of breastfeeding, but can't be bothered.
Babies in the first world are: 1) not exposed to that many dangerous pathogens to begin with; and 2) in the rare cases they do become infected, are easily treated with antibiotics, etc. Sure, breast milk has live immune cells, etc, but does that matter in any practical way?