From David Bowie, Manson took the whole gender ambiguous and sexually ambigious concept. Bowie famous for doing this with Ziggy Stardaust. Bowie had people guessing what he was or who he preferred to bed. Now none of that is really anyone’s business, in my not so humble opinion. Bowie was able to make you think about that subject in a way no one had or has since.
From Iggy Pop, Manson took the in your face and self mutilating image. Pop was known in the 70’s to do all sorts of harm to himself on stage. All of this was done under the influence of multiple psycho active substances. I am not excusing or supporting this behavior. This was done to shock the audience, and Manson defintely wants or wanted to shock his audience. Actually I think he wanted to shock the mainstrem society. Pop is considered many as the Godfather or Grandfather of Punk. Some of this behavior was adopted by that movement.