Join Date: Sep 2010
Location: In the shadows ...
I don't remember it being mentioned that cloning is illegal or forgotten within the Imperium. I thought certain Ordo Malleus personnel were cloned? I could be wrong. I also think, but its been awhile, that in the Word Bearer's Trilogy that they spoke of tank-bred sacrifices. If the forces of Chaos have the technology, then certainly the Imperium at the very least has examples of it, if not understands themselves.
But your point still stands -- there is no need. That would, however, be a hell of a hook on a chapter. Leaves them more open to corruption if that original genetic template should be altered or corrupted by some nefarious individuals.
The chaos gods abandoned Horus most likely because they saw the can of whoop ass coming their way and wanted out of the way so as not to get fucked up!