Legal threat in a handful of jurisdictions globally (China for example) has historically meant that that those jurisdictions would just be excluding themselves from the bitcoin open monetary network and the network continued.
We are now in a place where virtually all jurisdictions in the world will legally threaten bitcoin network participants. Over time there will be virtually no safe harbor globally. How many jurisdictions globally will turn a blind eye to unrestricted CSAM storage?
What do you expect a custodian, miner or node runner to do when threatened with legal action? Stand up tall in front of the man, try to run a "hidden" node somewhere, or run a fork that sanitizes the blockchain in some way?
The bitcoin frog will be cooked 1 CSAM image/video, jurisdiction and prosecution at a time. It will happen slowly, then suddenly when critical mass is achieved.