If I was on the jury I'd be 100% behind the argument. But someone outright stating that they're a pedophile and sexually attracted to children, it makes it that much more difficult for the jury to believe that the downloaded CP was in fact downloaded accidentally. But there's a still a lot that can be done e.g. if it can be shown that it was never viewed, and so forth.
Another potential problem may be if the prosecution in fact tries to argue that the child erotica - whatever that may be - in fact meets the federal definition of child pornography - that would kill the "knowingly" defense.