Man imagine trying to make "ethical child rape content" a thing. What were the lolicons not doing it for ya anymore?
As for how it's exactly as heinous, it's the sexual objectification of a child, it doesn't matter if it's a real child or not, the mere existence of the material itself is an act of normalization and validation of wanting to rape children.
Being around at all contributes to the harm of every child victimised by a viewer of that material.