Grace, I'm sorry if you've heard this before.  You're right, the
connection about lowered rates of child abuse probably has crossed the
minds and hearts of many lactation consultants.  When I was in nursing
school, I longed to do such research (starting with my middle child).
Anyway, I found one article:
        "Family Violence and Breast-feeding"  Archives of Family
        Medicine, Volume 4, July 1995, p. 650-652, author: Louise
        Acheson, MD, MS.
It's a small study, but it's a start.  Another way to go is to look at
the affect of prolactin on males not of the human species (it tends to
make them less violent).  In truth, I haven't researched such studies,
but have been told about them.
Good luck in your search and speech.  I'd love to pursue this, as I think
it is so incredibly important.
Lee-Ann Halbert, RN, BSN, JD, IBCLC