The problem is that Cameron may not be defending Akin's specific words in this specific instance, but he's certainly more than happy to defend the practice of what Akin did: he pretty much says that we should forgive Akin for telling lies, because Akin told those lies for a "good cause". He means well, Cameron says, so we should just ignore the fact that he got caught spouting sheer misogynistic nonsense about women's bodies being able to prevent pregnancy in the cases of "legitimate rape" (because then the "rape exception" for abortion would neatly and conveniently disappear into a Catch-22 - you can only get an abortion if you got pregnant from rape, but obviously if you got pregnant then it wasn't actually rape in the first place).
If you have to lie to defend your moral position about something, maybe it's not so moral to begin with.