neenz - bf babies are readmitted for treatment of dehydration when their bf has not been going well, this is correct. This is not a 'risk' of breastfeeding, but a 'risk' of poor support of breastfeeding. You might as well say that when people are admitted for food poisoning, this shows a risk of eating.
There is excess mortality among formula fed babies in the developed world - this is not controversial, and the studies are clear. The excess is mainly in SIDS and childhood cancers. It is a small, but measurable, elevated risk, which persists after controlling for social and other factors. It is negligible in individual terms, and no one should be frightened for an individual baby, but on a public health level, it shows. I can supply references.
The differential is larger in developing countries , as we know.
In the end, it depends on how important these issues of health are to you - there are many more issues, like breast cancer in the mother, the relationship aspects, the intelligence aspects, the environmental aspect, the enjoyment aspect. A small difference in risk in the west of say, ear infection, may not be worth worrying about, but if it's your kid who's got ear ache then maybe you feel differently. Even a few cases of breast cancer, or SIDS, or leukaemia, saved a year have an effect on our health costs, too, quite apart from the emotional effect on families.