The Minority Opinion
As others have stated, breast milk is liquid gold and it seems a shame to waste any on soap when it is better used to nourish babies, whether your own or others. However, I am also aware that it often happens that some milk is not appropriate to "serve" (due to items ingested or freezer shelf life).
I would have no problem using a breast milk soap produced from a stranger's milk. While it is true that breast milk (avoiding any confusion by abbreviating this as BM) is a bodily fluid and can transmit certain diseases if consumed. There is no risk of contracting any of them through soap. Saponification and cure aside, topical application is not conducive for any of the diseases that can be transmitted through breast milk.
http://www.babycenter.com/404_what-infections-can-be-passed-through-breast-milk_8840.bc
There is a greater statistical health risk posed in undergoing a blood transfusion. While carefully screened, the rare mishap occurs. Beyond that, there are individual immune responses and contaminants that cannot be screened for.
http://www.nhs.uk/Conditions/Blood-transfusion/Pages/Risks.aspx
There is no ick factor for me. If anything, I would assume that breast milk from a comparably hygienic human is less gross than that from the manure speckled and dirt crusted teats of a dairy cow.
The IceCreamist in London made news last year with its breast milk ice cream flavored with Madagascar Vanilla and lemon zest. They called it Baby Gaga and sold it for $23 per scoop. Nonetheless, they sold out in days! London authorities later confiscated the product while debating the controversial aspects.
http://www.huffingtonpost.com/2011/02/28/authorities-confiscate-breast-milk-ice-cream_n_829103.html
New York chef Daniel Angerer had enough milk to overrun their freezer when his daughter was born. They wanted to donate to a milk bank but could not do so until all his wife's prerequisite health screenings had been completed. Loathe to discard the "gold" and being an inquisitive chef, he made cheese for themselves and epicurean souls in search of truly exotic ingredients.
http://chefdanielangerer.typepad.com/chef_daniel_angerers_blog/2010/02/mommys-milk.html
I live in Austin and a local lollipop confectioner makes a breast milk flavored lollipop for children. It should be noted that the lolly is vegan and contains no actual breast milk. However, the description on their site indicates that plenty of donor milk was consumed by the confectioners in the process of trying to replicate the flavor.
http://www.lollyphile.com/products/breast-milk-lollipops
I do not have any kids myself, but assume that quite a few husbands have inadvertently sampled breast milk when they are forced to share their favorite toys with a little one. I myself was curious enough to sample the best friend's booby juice when she had my god child (from a glass, gutter brains).
Internet searches tell me that there are a number of people attempting to acquire breast milk for a variety of skin issues. While I can certainly understand the "intimate" quality of the product, my point (and I do have one) is that there are clearly a number of people besides myself that do not suffer from any "ick" factor.
