It is well documented that breastfeeding provides many health advantages for moms and babies. The incidence of upper respiratory infections is lower. The incidence of severe allergies, asthma, and type 1 (insulin dependent) diabetes is lower. The incidence of sudden infant death syndrome is lower. Moms who breastfeed even have a lower incidence of breast cancer. There's a myth that the baby weight comes off faster. Many women find that it helps. I didn't find that to be true - and many women don't.
In the US, where we have access to clean water, refrigeration, and infant formula that is virtually always safe if stored properly (there have been a few alarming -- even lethal, but rare -- exceptions), women can choose to feed formula without fear of the risks found in third world countries. They should be informed of the benefits they are giving up. They should be supported with good breastfeeding education and workplace accommodations, but I don't believe in badgering women who choose not to breastfeed.
Some moms have medical reasons for choosing formula. Those vary from a need to take medication not compatible with breastfeeding to breast surgery which interferes with milk production and let-down. In rare circumstances, the baby may have a genetic disorder which makes breastfeeding impossible, due to special dietary requirements.
Some women have psychological reasons. For example, women who were molested as children may find it difficult to even consider breastfeeding. Some women have work schedules which will not accommodate breastfeeding or even pumping. Some have tried with a previous infant and for one reason or another found it too discouraging to even try again. Some women wish to share the closeness of feeding times with the baby's father or other relatives.
Whether or not I agree with their reasons, I don't badger. I educate about options - like partial breastfeeding. I help them research medications to be certain that they have the latest information. If they wish, I can refer them to our social worker for help with other issues. I make sure that they know WIC provides food for breastfeeding moms in addition to formula for babies. Under the right circumstances, I'll even offer them a pump to help deal with engorgement.
In the end, I support their choice. Moms have a hard enough time without people trying to make them feel guilty about one more thing.
Yes, I wish everyone could breastfeed, but that isn't ever going to happen. Moms need to educate themselves and make the best choices for themselves and their babies - and nobody should jump to conclusions or behave in a hostile manner regardless of the way a particular baby is being fed.