All it would take is one overzealous prosecutor in a tiny jurisdiction to make a major issue of this that could literally disrupt the blockchain. That's a little scary.
There's some talk of hardforks here, so what about the idea of adding a 'delete method' in the next hardfork that could only be called by the same supermajority of witnesses necessary for an actual hardfork. Basically, a way to delete illegal content and reduce liability for witnesses by physically removing that content from the servers they maintain, without requiring witnesses to deploy new code like an actual HF. Is that even possible or just wishful thinking?
Thanks for opening the discussion on this, I think it might be a bigger deal than we realize.