There is obviously a difference between stealing and being inspired by something. Madonna has clearly been inspired by Monroe et al and takes inspiration for a lot of her imagery from other sources, but on the other hand she has lost a fair few lawsuits due to stealing music.
The answer is, no one is a saint. Fans tend to only notice what they want to, as do "haters", and at the end of the day it's all a bit petty isn't it??!! As far as I'm aware, Madonna has never stated to be completely original, as there is no such thing. Everything derives from something else, music, fashion, art, and I'm pretty sure Madonna (and Gaga, who has predictably been drawn into this as some kind of strange automatic defence-mechanism) will be the first to say that. They would probably be more than happy to go through what inspired them, but then they probably don't because then fans will end up killing each other, and they probably feel like they've got to live up to this expectation that must re-create the Big Bang every time they walk into a recording studio/photo shoot.