Babies cannot get HIV from breast milk, so there is no reason why they should no breastfeed. HIV is only transmitted through blood or sexual fluids. There are known benefits to breastfeeding, and all children should be able to enjoy these advantages. It can make the baby healthier and it can get immunities from the mother.
If something goes wrong and the mother's breast milk gets contaminated or she is bleeding but doesn't realize it, that can have a major effect on the child for the rest of his or her life. I believe that HIV infected mothers should pursue alternative methods to feed their children.