The paper says that the bitcoin blockchain already contains illegal content. In particular copyrighted material and possible child pornography. More precisely:
>an image depicting mild nudity of a young woman. In an online forum this image is claimed to show child pornography, albeit this claim cannot be verified
(I don't know exactly what it would mean to "verify" that an image contains child pornography, since in the US and UK at least some of the relevant laws refer only to what the image "depicts", not to the age of the people used in its manufacture. Either way, the copyrighted content seems enough to establish the illegality of the blockchain in principle.) It seems unlikely that any prosecutions will happen though, because blockchain technology has a lot of mainstream support.
>an image depicting mild nudity of a young woman. In an online forum this image is claimed to show child pornography, albeit this claim cannot be verified
(I don't know exactly what it would mean to "verify" that an image contains child pornography, since in the US and UK at least some of the relevant laws refer only to what the image "depicts", not to the age of the people used in its manufacture. Either way, the copyrighted content seems enough to establish the illegality of the blockchain in principle.) It seems unlikely that any prosecutions will happen though, because blockchain technology has a lot of mainstream support.