There are actually 3 separate issues related to Akin's comment:
1. The scientific basis for claiming a woman's body reacts to rape in a way that reduces the probability of pregnancy. I will not defend him on that count.
2. The use of the term 'legitimate rape'. This is, at best, a very poor choice of words. Even granting him the benefit of the doubt that he intended to distinguish actual rape from someone claiming rape when there was actual consent, the term 'legitimate rape' should never be used.
3. In context, he was attempting to support the position that abortion is wrong in ALL cases because the child is a innocent, living human being. If that is your position, how conception occurred is not relevant to the moral issue.