A British broadcaster was convicted of distributing CSAM because he replied to a message that contained CSAM, which they counted as distribution. They were motivated to catch him because they couldn't give him a jail sentence for possession due to it being a first offence.

If replying to a message in common law jurisdictions is counted as distribution, as in replying to the sender of the CSAM, then a motivated judicial system will absolutely count relaying transactions with CSAM in OP_RETURN as distribution.

They wouldn't even have to target everyone, just convict a couple of bitcoin influencers known to be running full nodes and the PR victory is sufficient to make Bitcoin not universal money in the eyes of the majority, confirmation bias that it is money for deviants and criminals, something many people already want to believe.

The equivalent before Core 30 is that someone snuck CSAM onto your machine in a format that you couldn't read without directly reproducing it from fragments, which is clearly not the same and could be the case with anyone's machine today given the prevalence of malware.

Now that bitcoin is an uncensored and unconstrained data transfer protocol it's going to be under a completely different kind of scrutiny.