Here are a few links in re: the HIV and breastfeeding issue.
http://www.unicef.org/programme/breastfeeding/hiv.htm
(Quite a few additional links here which also bear reading as they go more in-depth on the issue)
http://www.sciencedaily.com/releases...0329195658.htmhttp://www.sciencedaily.com/releases...0427200634.htm
I believe the current recommendation, given the death rate for infants/toddlers in the developed world from other causes of death -- is that infants be breastfed exclusively until six months of age (no supplementation at all in any form). The research shows that the HIV transmission likelihood occurs with the introduction of other foods (formula or solids). I believe then that with HIV mothers, at what point the baby hits six months, they are supposed to wean abruptly, as they introduce solids etc. They actually believe that while exclusively breastfed, there is a protective factor which reduces the likelihood of HIV transmission, in the mother's milk.
The rate of transmission of HIV to infants by their mothers after their birth (that is, via breastfeeding or etc., likely to have taken place once solids/formula were introduced) -- was 15%. The rate of death from diarrhea etc. from formula with unsafe drinking water etc. (the overall death rate from illnesses which would be treatable in the Developed world) is much higher.
So given all that - the HIV/AIDs argument is just not true. The recommendations differ between the USA and the Developing World, given the different risks facing infants in each.
In terms of the toxins in our foods and environment getting into our breastmilk -- we can control some of that with what we eat (i.e., organic foods) -- and cows are eating and breathing and drinking many of the same things we would be eating (in terms of toxins in the fertilizer used on the corn they were fed or etc.).
The thing to fix, is the toxins in the milk of all mammals -- not to swap to the milk of a different mammal in hopes that it won't matter that the cow's milk was not intended for the growth and sustenance of an infant human.
ETA: The possibility to exclusively breastfeed will vary from area to area - my aunt helped write the WHO breastfeeding code, has lived and worked with indigenous people in South and Central America, Asia, and parts of Africa -- where many women simply bring their children to work with them and can nurse while working, whether in fields or factories. It's going to vary. There are also of course, cultural variations in terms of infant feeding practices in general - ie, the practice of giving honey to newborns in India would certainly be detrimental with mothers who are HIV positive and wanting to breastfeed.