Of course you won't, if you accept that you, along with most women who wean thier babies early, will have to face the possibility that you stopped them from having something important. (Just as people who practice controlled crying or rigid routines refuse to believe that they might have done something potentially harmful)
As Kiskidee say, nursing a child for 4 years is not extended but natural or full term breastfeeding. Early weaning is one of the many unnatural things that have become "normal" in our society, along with expecting and "training" babies to sleep for 12 hour stretches alone in cots instead of frequently stirring for nightfeeds whilst sleeping next to thier mothers.
From my experience, of friends, mothers I have encountered whilst suporting bf and patients I have seen at work, those who wean early do it for two reasons, either because they think they have to(they have been told to stop by ill-informed health visitors, or to return to work etc) or because they wanted to. From that point of view it is early weaning which is practiced to please the mother, not "extended" breastfeeding.
Once you get past the first year breastfeeding becomes a relationship, and I am surprised you can't see this if you realy do have friends IRL who are nursing toddlers. Milk is the main food source during the first year, but after that breastfeeding is not just about calories and antibodies. Whilst the calories and fluids are still useful, the antibodies are definately important as your baby won't have a fully developed immune system until they are about 5 years old. But a nursing toddler gives them instant comfort, more than a cuddle can give, as nursing prompts the release of endorphins which soothe pain and aid sleep, it calms a cross or unhappy child better than a kiss, as Flowernat says the transformation is almost magical. The frustration of the terrible twos is somewhat replaced by two way communication and understanding, with silent apologies as mothers milk bridges the gap between the end of thier ability to tell us what they can't verbalise and our ability to understand what they are trying to say. And pre-school booster injections are a breeze when there's some booby afterwards to ease the sting of a nasty needle.
You chose to wean early, that's your perogative, and, I think it's great you gave your babies 12 months when so few get even 12 weeks. But this thread is all about supporting those of us who don't wean early, and to dismiss it as something we do because we like it is really simplistic and vaguely offensive. Not to mention wrong!
Monkies