The breastfeeding proponents are very good at making otherwise adequate mothers feel depressed.
It is also a very class based thing, middle class mothers tend to, and feel guilty about it when they can't, mothers from the lower socio-economic classes tend not to, and not feel so guilty about it. There is a definite element of snobbery amongst some middleclass parents who manage to breast feed their offspring until weaning, with a certain competitive element imagining that in some way there are huge benefits to their children, where there aren't.
Breast feeding is very important in the third world where clean water to make formula milk is hard to come by, in this country, the advantage is not so great. It is debatable how long you have to breast feed for for your child to accrue the benefits, but it's probably not a huge length of time (I think somewhere from 6 weeks to 3 months from memory).
Every last bit of this post is total sh*te.