I personally do not think the very subtle fact that your node didn’t relay the content in question wouldn’t save you if it’s downloaded on your node anyway.
If these fuckers want you you’re got no matter what you did or did not do. The hypothetical of arresting node runners en mass is a silly fiction in my opinion. The amount of resources it would take to try would be huge, there would be massive blowback, and they would understand this attack would have zero impact on the function of Bitcoin.
You think the feds want to investigate, try and potentially add thousands of non violent offenders to their already crowded “justice” system? It’s full of hardcore killers, gang bangers and serious criminals already. They don’t care about us running nodes. It’s just a very silly series of thoughts in my opinion.
I could be wrong but looking at the situation rationally I just don’t see it.