Men have nipples because they carry the X and Y chromosomes while women only carry X chromosomes. No man can be just a man because he comes from a woman who gave him the X chromosome. Most mammals have nipples. So when the female needs to go away for a breather the male can use his pacifier.
Males can and do lactate. It is an observed and repeatable phenomenon that males suplemented with female hormones can begin to lactate. It has also been historically documented of men breastfeeding babies occurring in the following areas: northern Burma, Scottish highlands, Baltimore, Maryland and Zaire. I also remember watching a documentary a few years back about a tribe somewhere where the men frequently lactate and participate in breastfeeding. You can find more info on this on various websites
of course GOd made Adam complete, with nipples. He made him and said "it is good", didnt he? How good would Adam look without nipples?