Tbh I don’t really have problem with criminals using bitcoin as money. Money should be neutral and if that means criminals will use it for monetary purposes, so be it.
I think it will always be possible for people to store and relay arbitrary data using the bitcoin network through exploits or unintended use cases but as long as bitcoin’s only intended function remains as neutral money then I think a lot of the social, moral, legal potential issues to do with arbitrary data will subside. In the case of the expansion of op_return, it is expanding bitcoins use case from just neutral money to also arbitrary data relay and storage.
Touching on the case where basically any data can be compressed into 20 bytes, this sort of tech would affect not just bitcoin but basically everything else, and so cp could be encoded in basically any transfer of data.