[Ekaros]

Similar reason with drugs. Use is not generally illegal, possession is. Possession is very easy to prove. Thus criminalization makes sense. Same goes for this type of material. If it stays private no one has idea and it won't be a problem. If it goes public, well now you have conclusive proof.

And the harm comes from sharing this material. So stopping people from possessing it as with lot of other material is not worse way to stop spread. Defence of I did not create it is not usable anymore.