The whole internet has a "great firewall". Kiwi Farms (whatever you think of them) was taken off the internet for a while due to (I think) backbone networks blocking/not resolving the DNS address. Any power that can be used for you can be used against you.
I agree, but for "violent crimes" I would think along the lines of the "hire a hitman" forums that were reputedly on the Silk Road dark web site before it was taken down.
