1) We're not talking about encrypted data.

2) Bitcoin does not support images at all, so it is impossible to store CSAM. Stegonography is another matter entirely (though even in that regard, there's no evidence of CSAM).

3) Spam is not usage, and Bitcoin relies on its users to protect it. WE are Bitcoin's antifragility.

4) Obviously I'm going to recommend OCEAN. Not only am I biased, but it's also better for Bitcoin. But the point is to mitigate this, I'm willing to concede even the would-be-worst pools to mine on are better than F2Pool right now.