The block size is limited and if filling blocks to 4mb is a burden to nodes, it is a burden whether it is spam or monetary transactions. It can’t be argued that full blocks is a threat to bitcoin when we’d all love to see them full of monetary transactions. CSAM is a fake argument meant to scare people. If storing bits that can be rendered to “illegal” pictures ruins bitcoin, it ruins it whether or not those pictures are easier or harder to render. I will never see any arbitrary data that is on my node because I will never go looking for it. You can’t make me a criminal by doing something unrelated to me then saying gotchya. My guess is that the whole CSAM issue is simply setting a narrative to try to justify governmental authority over Bitcoin. If it’s ever there, it will have been put there by someone trying to use it for that purpose and everyone reasonable will reject that framing. You stop pedophiles with a wood chipper not by pretending it ruins bitcoin. If someone puts sexual imagines hidden on the bitcoin blockchain, then the world can unite around finding and publicly executing that person.