Due process must be upheld because people are innocent until proven guilty.
It would set a bad precedent to allow arbitrary police seizure of assets without a court involvement.
… but I wonder if BoingBoing will post a follow-up should the City of London Police next obtain a court order to enforce the seizure?
There's no link to the affected websites or domain names that might allow us to form an opinion on whether the Police actions were plausibly reasonable - BoingBoing doesn't need to conduct balanced reporting, but it might be interesting to know whether the Police actions were outrageous, or whether the story is about the Police not following the correct procedure when acting against people for whom there's prima facie evidence of wrongdoing.
If the Police seized a totally arbitrary domain and redirected it to a Hollywood approved website, the Police would be liable to be sued themselves. Will the (unnamed) people affected here sue the Police, or do they want to keep the issue out of the courts in case it goes against them?
I don't necessarily support movie piracy, but I guess it's good news that we follow due process, because it will prevent inconvenient sites being silenced via the same mechanism in future, even if the people targeted by the City of London Police in this instance were clearly as guilty as sin.