If their policy was "we'll ban anyone we want for whatever reason." I'd respect that more because that's the truth.
Further troubling is how this is over what they believe to be illigal conduct. It may very well be, but now they're creating a precedent that they are capable of detecting and stopping it themselves outside the justice system.
This also doesn't stop kiwifarms or it's organizers. If there's illigal conduct, or even civil discovery, CF has to give up those details. All stopping Ddos support does is allows kiwifarms to receive Ddos.
No doubt they'll eventually take to tor and that doesn't have a good physical address to serve warrants to.